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Habitat Management Qualitative Risk Assessment : Water Column Oyster Aquaculture in New Brunswick

Habitat Management Qualitative Risk Assessment :
Water Column Oyster Aquaculture in New Brunswick
S. Bastien-Daigle, M. Hardy and G. Robichaud
Oceans and Science Branch
Fisheries and Oceans
Gulf Region
P.O. Box 5030
Moncton (New Brunswick) E1C 9B6
Canadian Technical Report of
Fisheries and Aquatic Sciences 2728
Canadian Technical Report of Fisheries
and Aquatic Sciences 2728
Habitat Management Qualitative Risk Assessment:
Water Column Oyster Aquaculture in New Brunswick
S. Bastien-Daigle, M. Hardy and G. Robichaud
Oceans and Science Branch
Fisheries and Oceans
Gulf Region
P.O. Box 5030
Moncton (New Brunswick) E1C 9B6
© Her Majesty the Queen in right of Canada, 2007.
Cat. No. Fs 97-6/2728E ISSN 0706-6457
Published by:
Oceans and Science Branch
Fisheries and Oceans
Gulf Region
P.O. Box 5030
Moncton (New Brunswick) E1C 9B6
Correct citation:
Bastien-Daigle, S., M. Hardy and G. Robichaud. 2007. Habitat Management Qualitative Risk
Assessment: Water Column Oyster Aquaculture in New Brunswick. Can. Tech. Rep. Fish.
Aquat. Sci. 2728 : vii + 72p.
OYSTER AQUACULTURE IN NEW BRUNSWICK ................................................................. 1
1.1 INTRODUCTION ........................................................................................................................ 1
1.2 REGULATORY CONTEXT............................................................................................................ 2
1.3 RISK ANALYSIS INITIATION ........................................................................................................ 3
2 DESCRIPTION OF WATER COLUMN OYSTER AQUACULTURE........................................ 6
2.1 CULTURE TECHNIQUES ............................................................................................................. 6
2.1.1 Suspended culture......................................................................................................... 7
2.1.2 Off-bottom culture.......................................................................................................... 9
2.1.3 Site preparation ............................................................................................................. 9
2.2 INSTALLATION .......................................................................................................................... 9
2.3 OPERATION ............................................................................................................................. 9
2.4 OYSTER SPAT COLLECTION..................................................................................................... 10
2.5 OVERWINTERING.................................................................................................................... 10
2.6 HARVESTING.......................................................................................................................... 10
2.7 PREDATOR CONTROL............................................................................................................. 11
2.8 DECOMMISSIONING ................................................................................................................ 11
3 RISK MANAGEMENT FRAMEWORK.................................................................................... 12
3.1 SCALE OF NEGATIVE EFFECTS................................................................................................. 13
3.2 SENSITIVITY OF FISH AND FISH HABITAT. .................................................................................. 14
4 ECOLOGICAL RISK ASSESSMENT..................................................................................... 16
4.1 EFFECTS CHARACTERIZATION ................................................................................................. 16
4.1.1 Potential pathways of effects....................................................................................... 16
4.1.2 Potential sources ......................................................................................................... 18
4.2 EXPOSURE CHARACTERIZATION .............................................................................................. 18
4.2.1 Adversity of exposure and effects ............................................................................... 18
4.2.2 Scale and intensity of exposure................................................................................... 25 Oyster production in the Maritimes................................................................................ 25 Scale of oyster aquaculture production.......................................................................... 26
4.2.3 Relative intensity of aquaculture production................................................................ 26
4.2.4 Potential co-occurrence............................................................................................... 29
4.3 SENSITIVITY OF FISH HABITAT ................................................................................................. 31
4.3.1 Characteristics of estuaries in N.B. ............................................................................. 31
4.3.2 Sensitivity characterization .......................................................................................... 32
4.3.3 Sensitivity of fish species............................................................................................. 33
4.3.4 Sensitivity of submerged aquatic vegetation............................................................... 33
4.4 SIGNIFICANCE OF ECOLOGICAL RISK........................................................................................ 39
4.4.1 Biodeposition ............................................................................................................... 39
4.4.2 Carrying capacity......................................................................................................... 41
4.4.3 Nutrients ...................................................................................................................... 42
4.4.4 Submerged aquatic vegetation.................................................................................... 43
4.4.5 Species interactions..................................................................................................... 44
4.5 CONCLUSION OF ECOLOGICAL RISK ASSESSMENT ................................................................... 46
5 NET ECOLOGICAL BENEFIT ANALYSIS............................................................................. 48
5.1 HISTORICAL STATE OF OYSTER POPULATIONS.......................................................................... 48
5.2 CHARACTERIZATION OF REFERENCE STATE ............................................................................. 51
5.3 ECOLOGICAL BENEFIT CHARACTERIZATION .............................................................................. 51
5.4 COMPARISON OF ALTERNATE STATES...................................................................................... 53
5.5 SIGNIFICANCE OF ECOLOGICAL BENEFITS ................................................................................ 53
5.6 CONCLUSION ON NET ECOLOGICAL BENEFIT ANALYSIS............................................................ 55
6 RISK MANAGEMENT ASSESSMENT................................................................................... 57
6.1 IDENTIFICATION OF APPROPRIATE RISK MANAGEMENT OPTIONS ................................................ 57
6.2 RISK COMMUNICATION ........................................................................................................... 58
6.3 RISK MONITORING, REPORTING AND REVIEW............................................................................ 58
7 CONCLUSIONS...................................................................................................................... 60
8 ACKNOWLEDGEMENTS....................................................................................................... 62
9 REFERENCES........................................................................................................................ 63
FIGURE 3 - DFO HABITAT MANAGEMENT PROGRAMS RISK ASSESSMENT MATRIX............................................ 12
2007; N=658)........................................................................................................................................ 30
1987, DFO 2003B). ..............................................................................................................................49
(FROM NEWELL 2004)............................................................................................................................ 56
TABLE 2 - ATTRIBUTES USED TO DEFINE SENSITIVITY OF FISH HABITAT ............................................................. 15
2003).................................................................................................................................................... 28
LAWRENCE, 2001-2002......................................................................................................................... 30
1988) COMPARED TO PRESENT AQUACULTURE AND FISHERY LEVELS........................................................ 50
2005).................................................................................................................................................... 52
The Department of Fisheries and Oceans Canada (DFO) is responsible for evaluating
potential environmental impacts on fish habitat associated with project development.
Aquaculture of the native oyster (Crassostrea virginica) has been expanding in gulf New
Brunswick’s (N.B.) coastal communities, thus, a qualitative risk assessment was initiated. This
involves an evaluation of water column oyster aquaculture and its interactions with fish habitat,
as defined in the Policy for the Management of Fish Habitat, by integrating a thorough review of
the current scientific information and a description of the oyster aquaculture industry. This
assessment follows the work of the National Advisory Process which characterized the potential
environmental risks of bivalve aquaculture in the marine environment. That scientific review is
complemented with technical data as well as additional information to specifically characterize
the potential effects of oyster aquaculture in N.B. The present qualitative risk assessment is
intended to assist habitat managers in their decision-making process and is based on the
Habitat Management Program Risk Management Framework. The framework provides a
structured process for characterizing the potential risks and assessing their significance in
regards to the productive capacity of fish habitat. An Ecological Risk Assessment and a Net
Ecological Benefit Analysis are used to make determinations as to the effects and functions,
respectively, of water column oyster aquaculture in gulf N.B. Using the risk assessment, we
conclude that the overall “scale of potential negative effects” of water column oyster aquaculture
and the “sensitivity of fish and fish habitat” correspond to a low-risk activity which is not likely to
significantly harm the productive capacity or the ecological integrity of fish habitat. Moreover, our
analysis suggests that oysters in aquaculture can potentially be of significant benefit to these
estuaries and can help to restore many important ecological functions which were reduced
following the historical decline of natural populations. Given the nature of this activity, we
conclude that the risks associated with water column oyster aquaculture can be managed in a
sustainable manner with adequate planning and mitigation measures through an adaptive
management approach.
Le Ministère des Pêches et des Océans du Canada (MPO) est responsable d’évaluer les
effets environnementaux potentiels des projets de développement sur l’habitat du poisson.
L’aquaculture de l’huître indigène (Crassostrea virginica) est une activité en croissance au
Nouveau-Brunswick (N.-B.). Pour cette raison, une évaluation qualitative du risque de cette
activité a été entreprise. Une évaluation des interactions entre l’ostréiculture en colonne d’eau
et l’habitat du poisson a été effectuée, tel que définie sous la Politique de gestion de l’habitat du
poisson, par l’entremise d’une revue d’informations scientifiques et une description de l’activité
ostréicole. Cette évaluation fait suite au processus officiel d’avis scientifique qui a caractérisé
les risques environnementaux potentiels de la culture marine des bivalves. Cette revue
scientifique ainsi que d’autres études et informations techniques ont été utilisées afin de
caractériser plus spécifiquement les effets de l’ostréiculture dans la colonne d’eau au N.-B.
L’évaluation qualitative du risque a comme objectif d’aider les gestionnaires dans le processus
de prise de décisions selon le Cadre de gestion de risques du Programme de gestion de
l’habitat. Ce cadre offre un processus structuré qui permet de définir les risques et déterminer
leur importance en fonction de la capacité productive de l’habitat du poisson. Une évaluation du
risque écologique et une analyse du bénéfice écologique net ont été utilisées afin de déterminer
les effets et les fonctions, respectivement, de l’ostréiculture dans la colonne d’eau au N.-B.
Cette analyse nous a permis de conclure que l’échelle des répercussions défavorables de
l’ostréiculture en colonne d’eau et la vulnérabilité du poisson et de l’habitat du poisson
correspondent à une activité ayant un risque faible qui a peu de probabilité de nuire de façon
importante à la capacité de productivité ou à l’intégrité écologique. De plus, notre analyse
suggère que les huîtres en aquaculture peuvent potentiellement jouer un rôle bénéfique dans
ces systèmes et servir à combler plusieurs fonctions écologiques qui ont été perdues suivant les
déclins historiques des populations d’huîtres. Étant donnée la nature de cette activité, nous
concluons que les risques associés à l’ostréiculture dans la colonne d’eau peuvent être gérés de
manière durable à l’intérieur d’un cadre de gestion adaptive qui comprend des mesures
adéquates de planification et d’atténuation des impacts.
1.1 Introduction
The Habitat Protection and Sustainable Development (HPSD) section of the Department of
Fisheries and Oceans Canada (DFO) is responsible for evaluating potential environmental
impacts on fish habitat associated with project development under the Habitat Management
Program (HMP). DFO has been conducting environmental assessments of aquaculture impacts
to fish habitat on a site-by-site basis under Section 35 of the Fisheries Act and coordinating the
review of other federal authorities (FA) and expert authorities under the Canadian Environmental
Assessment Act (CEAA). Given that the development of oyster aquaculture is among the
growing activities in New Brunswick’s (N.B.) coastal communities, the following qualitative risk
assessment was conducted under the guidance of the HMP Risk Management Framework. This
assessment of water column oyster aquaculture (i.e. suspended or off-bottom culture) integrates
a thorough review of the relevant scientific information and a characterization of “works” (defined
by CEAA) associated with oyster aquaculture, as it relates to fish and fish habitat and the Policy
for the Management of Fish Habitat.
Risk is unavoidable and present in virtually every human situation. It is present in our daily
lives, and in public and private sector organizations. The World Trade Organization (WTO)
defines Risk Analysis as a “systematic way of gathering, evaluating, recording and disseminating
information leading to recommendations for a position or action in response to an identified risk”.
Risk can be defined as a function of the probability of an adverse effect and the severity of that
effect. In fact, this approach is used worldwide to manage the ever-changing uncertainties
associated to human health, international trade, food safety, etc. (e.g. World Health Organization
(WHO), WTO, Food and Agriculture Organization (FAO) Sanitary and Phytosanitary agreement,
Hazard Analysis and Critical Control Point (HACCP)). Thus, a Risk Analysis is a tool intended to
provide decision-makers with an objective, repeatable and documented assessment of the risks
posed by an action. This approach recognises that every facet of life involves risks which can
range from significant and adverse to negligible and inconsequential. Risks needs to be
characterized, their significance assessed and thereafter managed to ensure a degree of
comfort and control despite the uncertainties.
In context of the HMP Risk Management Framework, we define “Risk” as an event that
has a specific likelihood of occurrence and identifiable impacts on the productive capacity of fish
and fish habitat. A risk-based approach allows habitat managers to prioritize and focus efforts
on regulating the activities which are considered to have the greatest potential impact to fish and
fish habitat. This entails the review of available relevant information in order to categorize the
risks associated with development proposals and associated management options. Through an
objective and science-based decision-making process, activities are rated according to risk (e.g.
low, medium and high) and then evaluated against the sensitivity of habitat and the scale of
effects. This approach recognizes that high risk projects need to be managed differently than
low risk projects. It is from this perspective that the following qualitative risk assessment of
water column oyster aquaculture was prepared.
In collaboration with Maritimes Region and National Headquarters, a panel of scientists
was brought together in 2006 under the National Science Workshop: Assessing Habitat Risks
Associated With Bivalve Aquaculture in the Marine Environment National Assessment Process
(NAP), to identify and characterize the potential environmental risks of bivalve aquaculture in the
marine environment. The NAP was based on the peer review of working papers that addressed
the identification, prediction, and measurement of the effects of marine bivalve aquaculture. The
majority of the information presented at the workshop was based on the suspended culture of
mussels on the east coast of Canada, but provided some indications as to the risk associated
with bivalve culture in general. We have since undertaken the task of integrating the scientific
advice which was relevant to water column oyster aquaculture into this Risk Assessment based
on these frameworks and international definitions.
1.2 Regulatory context
In 1999, the Navigation Water Protection Program (NWPP) and CEAA recognized the
need to consider aquaculture structures as having a fixed location and thus constituting a “work”
under the Navigable Water Protection Act (NWPA). Therefore, these operations needed to be
reviewed and approved under the NWPA. This led DFO to become a Federal Responsible
Authority (FRA) for the review of aquaculture works under CEAA for the NWPP and a more
formal federal review process which includes a fish habitat assessment under the habitat
provisions of the Fisheries Act.
Following organizational changes in 2004, the responsibilities of FRA were transferred to
Transport Canada (TC), with HPSD remaining involved on aquaculture files. To assist with that
transition, DFO and TC developed a Memorandum of Understanding (MOU) whereby it was
proposed that DFO help TC in the development of a Replacement Class Screening Report
(RCSR) under section 19 of the CEAA to implement a more coherent approach in Environmental
Assessment (EA) of these works. Rather than completing an EA for each project, the Act allows
for the EA of some repetitive projects to be streamlined through the use of a class screening
report. This signifies that if a project qualifies and meets the criteria set forth in the RCSR, it may
not need an individual EA. This kind of report is built on and uses the knowledge accumulated
through past environmental assessments of a given type of project. The class screening
approach is considered compatible with an earlier proposal made by DFO to the New Brunswick
Shellfish Aquaculture Environmental Coordination Committee (NBSAECC) operating under the
1995 Canada-New Brunswick MOU on aquaculture to develop an integrated shellfish
aquaculture planning exercise. The Bay-by-Bay planning approach for aquaculture development
was proposed to the Province of New Brunswick (aquaculture leasing and licensing is managed
by the Province), in order to pre-define suitable areas for aquaculture based on an analysis of
conservation and regulatory concerns of provincial and federal departments. It was presented to
federal expert departments as a means to address cumulative impacts and inter-governmental
regulatory concerns. The concept was accepted by the NBSAECC.
An initial pilot-project for the bays of Tabusintac and Richibucto was initiated in 2004. GIS
databases were used to identify Valued Ecosystem Components (VECs) as well as potential
conflicts with aquaculture works. Ecological reviews of the bays and layers of information, such
as locations of bird colonies, avian species at risk, migrating and staging areas for waterfowl,
fish habitat, wetlands, dunes, salt marshes, fisheries etc. were presented on maps. Potential use
scenarios in conjunction with various management options were evaluated. This approach
combined a number of GIS databases with current knowledge on user impacts to create an
analytical tool to guide towards sustainable development. Zones were subsequently defined
where shellfish leases could be best located to avoid potential spatio-temporal interactions with
VECs. After a review of the pilot project results, the New Brunswick Department of Agriculture
and Aquaculture (NBDAA) decided to continue the planning project, in collaboration with DFO
and TC, for the remaining bays on the eastern coast of the Province.
1.3 Risk Analysis initiation
The current Risk Assessment expands on the scope of the evaluation of this activity and
integrates the regulatory context which was required to support decision-makers in their review
of water column oyster aquaculture works as they relate to fish and fish habitat. This is also
compatible within the larger context of a Bay Management Framework developed in
collaboration with the Province of New Brunswick. The geographic area for which the risk
assessment was needed is Gulf New Brunswick (N.B.), but could also apply to Prince Edward
Island (P.E.I.) and Gulf Nova Scotia (N.S.). In order to alleviate the remaining text, oyster
aquaculture in N.B will refer to the Gulf portion along the eastern shore of N.B. and exclude the
Bay of Fundy. The risk assessment was conducted to provide information to habitat managers
about the potential effects of oyster aquaculture works and management options.
The format used for this assessment was inspired in part by the US Environmental
Protection Agency Guidelines for Ecological Risk Assessment (ERA) (US EPA 1998). These
types of tools are used to identify and characterize potential risks of the activity and to make a
determination as to their significance as they relate to the productive capacity of fish habitat. In
the HMP Risk Management Framework, this assessment is important for qualifying the residual
negative risks after mitigation measures as well as subsequently determining options to manage
the risks specific to the activity.
Additionally, because oysters in nature are recognized as providing beneficial ecological
services and are often used as a compensation option for other works, a Net Environmental
Benefits Analysis (NEBA) approach, as proposed by the US Department of Energy, was used to
look at the potential gains minus the potential environmental costs of this activity (US
Department of Energy 2003). Although the NEBA is not factored in to the HMP Risk
Management Framework, we believe that a NEBA is consistent with the “Net Gain of Habitat for
Canada’s Fisheries Resources” in the Policy for the Management of Fish Habitat. The policy
states that the objective is to: “Increase the natural productive capacity of habitats for the
nation's fisheries resources, to benefit present and future generations of Canadians”. We also
believe that a NEBA can play a valuable role in considering the development of integrated
management plans and in moving towards to DFO’s emphasis on an ecosystem approach.
The following diagram (Figure 1) illustrates how the two frameworks are used in parallel in
this risk assessment on water column oyster aquaculture.
Figure 1 - Frameworks for Ecological Risk Assessment and Net Ecological Benefit Analysis
In the Maritimes, oyster culture is an activity which is usually practiced on a technically
simple small-scale level. This activity is spread throughout coastal areas along the southern Gulf
of St. Lawrence. In N.B, operations are mainly family owned; with a single proprietor for whom
this is not their main occupation (75-90% of their income originates from other sources). The
majority of these operations employ fewer than six employees, on a seasonal basis, but this
number may range from one to sixteen employees. Most owners operate only one or two leases
(Bastien-Daigle & Friolet 2006).
Procedures and activities associated with oyster culture in N.B. estuaries have a
substantial history and record of development. Oyster aquaculture projects in New Brunswick
have similar design, construction, operation and decommissioning characteristics. The following
section summarizes the nature of the industry; the reader can consult Doiron (2006) for more
detailed descriptions. Prince Edward Island and Nova Scotia use similar water column growing
techniques. Prior to completing this risk assessment, a phone survey was conducted with
individual growers to obtain an accurate picture of equipment and techniques currently in use
(Bastien-Daigle & Friolet 2006).
2.1 Culture techniques
Unlike many parts of the world and the western region of Canada, where the exploitation
of native species contributes little to commercial production (FAO 2005), the harvest and
aquaculture of oysters along the Atlantic coast of Canada and the United States of America
relies on a native species, the eastern oyster Crassostrea virginica. This species is found along
the entire Northwest Atlantic seaboard, from Louisiana to N.B. with a large population in the
southern Gulf of St. Lawrence (sGSL) (Kennedy et al. 1996).
In water column aquaculture, oysters are floated or suspended in the subtidal zones.
Raising oysters above the substrate and placing them in bags or cages serves to enhance water
circulation, water temperatures, and food availability. This in turn improves growth and
decreases predation rates. Oysters grown in this manner are generally kept at low densities to
help ensure that they can reach market-size within 3 to 4 years, rather than the 5 to 8 years
normally required when grown on the substrate (DFO 2003b).
Presently, a variety of water column culture methods are used in N.B for growing oysters.;
these include longline culture using bags, trays, or rope strings, or cages, and off-bottom culture
using bags on French tables or on trestles. Provincial authorities define suspended culture as a
form of aquaculture conducted in the water column or at the water’s surface, where the
structures are anchored but can float or move with the tides. They define off-bottom culture as
being conducted in the water column where the structures are fixed in place on the substrate
and do not move with the tides. The present risk assessment covers these two categories of
techniques, commonly referred to as water column oyster culture. It does not include bottom
culture, which is conducted directly on, or in, the substrate of an aquaculture site.
2.1.1 Suspended culture
Grow-out bags made of high density, UV-resistant polymer mesh (often referred to by the
manufacturer’s name, such as Vexar or Durethene® bags) are used to contain the oysters.
The bags are either equipped with individual floats and attached to a longline system or inserted
in a cage structure equipped with floats. Bags measure 85 cm (long) by 40 cm (wide) by 10 cm
(high). The density of oysters in the bags is progressively reduced over the 3-4 year grow-out
period as the oysters grow (Doiron 2006). Initially, 15-25 mm oysters are placed at densities of
1000-1500 oysters per bag (2-3 kg). In the final year of production, oysters typically measure
50-75 mm and are held at densities of 200-250 per bag (4-6 kg) to ensure adequate growth and
a desirable shape (i.e. choice or fancy grade rather than commercial or standard) (Doiron 2006).
In the longline system, grow-out bags are lie flat on the surface of the water with one buoy
on each side and secured by parallel lines anchored to the bottom (Figure 2). The most common
design usually consists of two rows of approximately 50 floating bags, but many variations of this
system can be observed. Two main anchors maintain the longline in a fixed location; these
consist of concrete blocks, metal anchors or screw anchors. The lines are kept separated by
spreader bars installed approximately every ten bags. Growers can adjust the buoyancy of the
grow-out bags by changing the location of the buoys on the bags. Each longline system
measures approximately 60 m from anchor to anchor, and is spaced 6-10 m from other longlines
to provide water circulation around the bags and boat access for regular maintenance. Growers
typically install 15 to 20 longlines per hectare. Longlines are usually oriented along the most
appropriate axis to reduce wear from tides and currents on equipment.
Cages are made of a plastic coated wire-meshed material (similar to the Aquamesh used
in many lobster traps) and are designed to contain between 2 to 6 grow-out bags; six being the
most common configuration. The grow-out bags are placed in divided sections of the cage,
which function as drawers. In order to ensure adequate water circulation, no more than two bags
are placed over one another. Each cage is equipped on the upper side with two buoys allowing it
to float immediately below the water surface. Buoys can be made of a variety of materials,
including Styrofoam and PVC. The cages are secured either by using single anchors or by
attaching them to longlines. Generally, growers will install 12 cages per 50 m longline with a
maximum of 20 lines per hectare (240 cages/ha). As above, lines are separated by a corridor to
allow boat access.
Space between bags
Figure 2 - Description of the longline structures used in N.B. (modified from Doiron 2006)
A less common suspended technique is known as rope culture, whereby clusters of
oysters are attached directly to a rope at regular intervals (without any housing). Ropes are
suspended in the water column or floated at the water surface level using specifically designed
supports, which function similar to longline systems. Oysters cultured on rope remain
submerged at all times.
2.1.2 Off-bottom culture
Oyster tables, also known as French tables, consist of a metal rod structure on which
grow-out bags containing the oysters are supported. This platform raises the bags sufficiently to
ensure water circulation around the oysters. Depending on the site, oysters can be uncovered
during each tidal cycle or remain constantly submerged. Another off-bottom technique consists
of raising the oyster bags on runners or pipes placed on the sediment. Both of these techniques
typically require setting the structures in sections of the lease with little or no eelgrass to ensure
proper water circulation. Oyster tables and runners are removed at the end of the growing
season to avoid ice damage.
2.1.3 Site preparation
Unlike some types of on-bottom shellfish aquaculture that require extensive bottom
preparation (e.g. dragging, additions of gravel, dredging, removal of vegetation, etc.), no specific
site preparation activities are required for water column oyster aquaculture sites other than
installing the equipment and anchors.
2.2 Installation
The installation of structures is generally done from a boat or from the ice surface during
winter. For longlines, anchors are installed either directly on the marine sediment (concrete
blocks) or driven into the sediments (anchors). In general, the anchoring system is designed to
be permanent. French tables and runners are installed directly on the substrate but are
removed seasonally.
2.3 Operation
Maintenance of the inventory includes stock rotation and reducing the density of oysters to
ensure optimum growth and quality; this may occur 2 to 3 times during the growing season. As
the bags float at the surface of the water, with one side submerged and the other exposed to air,
fouling by epifaunal plants and animals can be removed simply by turning the bag (180°) to
allow the attached organisms to desiccate or by pressure washing. The frequency of this
maintenance depends on the growth of epifauna which varies during the season; being more
pronounced in the summer and less so in the fall. In general, air drying takes a few days. Oyster
culture does not require food supplements, treatment with pharmaceuticals, disinfectants, or
2.4 Oyster spat collection
Oyster spat or oyster seed can be collected by the producer or can be purchased from
other local growers. Oyster seed can only be collected from approved oyster collection areas or
on private leases. Oysters typically spawn between early and mid-July depending on latitude
and annual conditions. A variety of collectors are used to attract oyster larvae, which
preferentially settle on clean and textured surfaces. It is critical to deploy these collectors in the
appropriate areas at the correct time. After approximately two to three weeks of drifting in the
currents, competent larvae cement themselves to the collector’s surface. Afterwards, when
oyster seed reach a sufficient size, the collectors are transferred to the lease (if seed are not
collected from the lease area itself). Depending on their size, the seed oysters are stripped from
the collectors in the fall or the following spring, sorted by size and transferred to the grow-out
2.5 Overwintering
In much of gulf N.B., the upper water column freezes in winter. In order to protect the
oysters, structures must be overwintered in below the depth to which the ice can extend or in
areas that are not prone to ice jams, or frequent ice movement. Typically, oysters are moved to
the deepest portion of the aquaculture site and sunk to the bottom during the winter months.
This period corresponds to a period of dormancy for the oysters, where filtration and feeding
effectively stop.
Oysters are overwintered in bags or cages. The longlines can be either submerged below
the surface, deep enough to avoid the ice, but not touch the seabed (using weights to counter
the buoyancy of the equipment), or the floats are removed from the bags/cages and the
structures are allowed to lie on the substrate. Sunken lines are located by GPS or by
triangulation to facilitate retrieval during winter harvesting or for re-suspension. Oysters are re-
deployed to the grow-out site the following spring; re-suspension is carried out as soon as
possible after ice break-up.
2.6 Harvesting
Harvesting occurs when oysters reach marketable size. During the ice-free period,
harvesting is generally done by boat; grow-out bags are light enough to be removed by hand
from the structures and loaded onto vessels. The heavier cages may require a winch to hoist
them onto the boat. The transport boat typically unloads the bags and product at a landing from
where it is delivered by truck to a processing facility.
During the winter harvesting, the overwintering sites are typically accessed by all terrain
vehicles or snowmobiles. An access hole is cut through the ice with a chain saw or auger and a
portion of the stock is retrieved manually or with the use of manually-operated hydraulic
equipment. Divers may be required to assist in retrieval of the stock.
2.7 Predator Control
Predators are of greatest concern during the spat collection phase when oysters are small
and not protected within the grow-out bags. In some cases, predators such as crabs and starfish
are controlled by dipping the collectors for a few seconds in a freshwater or diluted lime bath.
Competitors or predators found within the grow-out bags are manually removed during regular
maintenance activities.
In gulf N.B. oyster culture, there are no control measures which could harm marine life
such as birds or mammals (i.e. anti-predator nets, acoustic scaring devices, etc.). The need for
predator removal is rare in the case of off-bottom oyster culture, because the stock is protected
within the grow-out structure.
2.8 Decommissioning
Within 90 days of cessation of aquaculture activities, the holder of the aquaculture
occupation permit or the aquaculture lease is required under provincial jurisdiction (N.B.
Aquaculture Act, 1988, c. A-9.2, and 91 158 of the N.B. Regulation under the Aquaculture Act) to
restore the site to the satisfaction of the Minister. If the holder does not restore the aquaculture
site within the prescribed time or in a manner considered satisfactory by that authority, NBDAA
will have the site restored, and the holder will be liable for all restoration costs.
The Risk Management Framework is intended to provide a structured approach to decision-
making that takes into account the concepts of risk, uncertainty and precaution. A Risk
Assessment is a process used to determine the level of risk that residual effects pose to fish and
fish habitat based on the information currently available. Risk Assessments are used to
determine the technical parameters that are useful and feasible for risk management.
To assess risk to fish and fish habitat, one must consider the severity of the effects in the
context of the sensitivity of fish and fish habitat being affected by the activity. The Risk
Assessment Matrix (Figure 3) incorporates these two factors in order to characterize the level of
risk posed by the development proposal on the productive capacity of fish habitat. The rationale
used to locate the residual effects on the matrix forms the basis for decision-making.
No impact - no Fisheries Act requirements
Highly sensitive
Sensitivi ty of fish an d fish habitat
Mo derately sensitive Low sensitivity Not fish
Scale of
Operational Statements, letters of advice, best management
practices, guidelines, certification, partnership
Streamlined authorization process,
class authorizations
Site specific review and
negative effects
Figure 3 - DFO Habitat Management Program’s Risk Assessment Matrix
3.1 Scale of negative effects
The following attributes are used to scale residual effects on the y-axis of the risk
assessment matrix (Table 1) and are adapted to aquaculture. Ratings are assigned to evaluate
the predicted effect of the activity. For every effect, the degree of adversity of each attribute is
assessed and this helps to determine the overall residual effect significance.
Table 1 - Attributes used to describe the scale of negative effects to fish habitat
Criteria Importance level rating
Low Medium High
Magnitude Localized effect on
specific group,
habitat, or
ecosystem, returns
to pre-Project levels
in one generation or
less, within natural
Portion of a
population or
habitat, or
ecosystem, returns
to pre-Project levels
in one generation or
less, rapid and
change, temporarily
outside range of
natural variability
Affecting a whole
stock, populations,
habitat or
ecosystem, outside
the range of natural
variation, such that
communities do not
return to pre-Project
levels for multiple
Geographic Extent Limited to
footprint and vicinity
Limited to
aquaculture lease
and vicinity
Extends beyond the
aquaculture lease
Duration of Effect Less than one
Less than one year A year or longer
Frequency of
Occurs on a
monthly basis or
less frequently
Occurs on a weekly
Occurs on a daily
basis or more
Reversibility Effects are
reversible over
short term without
active management
Effects are
reversible over
short term with
active management
Effects are
reversible over
extended term with
active management
or effects are
3.2 Sensitivity of fish and fish habitat.
The sensitivity of fish and fish habitat (represented by the x-axis of the matrix) can be
defined in relation to the degree and duration of damage caused by a specified external factor.
Sensitivity may refer to the structural fragility of the entire habitat in relation to a physical impact,
or to the intolerance of individual species comprising the habitat to environmental factors, such
as exposure, salinity fluctuations or temperature variation.
Habitat can be defined as "the structural component of the environment that attracts
organisms and serves as a center of biological activity" (Peters & Cross 1992 cited in Auster &
Langton 1998). In this example, habitat would include the range of sediment types (e.g. mud,
sand, pebble, etc.); and bed forms (e.g. sand waves and ripples, mudflats, etc.) as well as the
co-occurring biological structures (e.g. shell, burrows, submerged aquatic vegetation, etc.).
Defining sensitivity for all these components is problematic. Ideally, models of sensitivity indices
for specific habitats, communities, and key taxa-based on the effects of specific activities, levels
of effort, and life history patterns (of both fish and taxa which serve a habitat function) would be
developed (Auster & Langton 1998). Such indices are not currently available; as a substitute, the
Habitat Management Policy recommends the use of a matrix analysis to determine the
sensitivity of fish and fish habitat.
This matrix uses general qualifiers to describe fish and fish habitat attributes (summarized
in Table 2). Sensitivity is defined in terms of species or habitat susceptibility to changes and
perturbations as result of an activity or modifications in environmental conditions, such as
suspended sediments, water temperature or salinity. Dependence is defined in terms of the use
of habitat by fish species; for example, some species may be able to spawn in a wide range of
habitats, while others may have very specific habitat requirements. Rarity is defined in terms of
the relative strength (abundance within a range) of a fish population or the prevalence
(ecological redundancy) of a particular type of habitat in a community. Resilience refers to the
ability of an aquatic ecosystem to recover from changes in environmental conditions.
Table 2 - Attributes used to define sensitivity of Fish Habitat
Criteria Importance level rating
Low sensitivity Moderately sensitivity Highly sensitivity
Sensitivity Species/habitat
present are not
sensitive to change
and perturbation
present are moderately
sensitive to change
and perturbation
present are highly
sensitive to change
and perturbation
Dependence Not used as habitat; or
used as migratory
habitat only
Used as feeding,
rearing, and/or
spawning habitat
Habitat critical to
survival of species
Rarity Habitat/species is
abundant within its
range or community;
ecological redundancy
is widely present
Habitat/species has
limited distribution; is
confined to small
areas; ecological
redundancy is present
Habitat/species is rare;
ecological redundancy
is absent
Resiliency Species/habitat is
stable and resilient to
change and
Species/habitat is
stable and can sustain
moderate level of
change and
Species/habitat is
unstable and not
resilient to change and
Ecological risk assessment is based on the characterization of the potential effects and
characterization of exposure (US EPA 1998). Effects are linked to ecosystem receptors and
stressor-response profiles. Exposure is linked to potential pathways of effects, potential sources
and potential co-occurrence. Exposure is also related to the scale and intensity of activities.
The scope of this ecological risk assessment focuses on water column oyster aquaculture as it
relates to fish and fish habitat.
4.1 Effects characterization
4.1.1 Potential pathways of effects
The analysis of the potential pathways of effects is largely based on information contained
in the NAP documents ( Anderson et al. 2006, Chamberlain et al. 2006, Cranford et al. 2006,
DFO 2006, McKindsey et al. 2006a, Vandermeulen et al. 2006) as well as the Statement of
Knowledge (SoK) reports (DFO 2003a). These various papers, which undertook comprehensive
reviews of the science available, provide extensive details on shellfish aquaculture in general
and aid in the specific characterization of the potential effects of water column oyster
aquaculture. Consequently, the following sections only discuss some of the major points in a
cursory manner.
Many of the adverse effects and concerns in the conclusions from the NAP were linked to
studies conducted in Tracadie Bay, P.E.I. Much of the discussion and most of the modeling
results presented focused on the evaluation of carrying capacity for this bay, which is one of the
most intensively cultured and studied bays for shellfish aquaculture in the Gulf Region.
Approximately 40% of Tracadie Bay’s surface is leased for mussel cultivation, with an annual
mussel production of 2,000 t. From 1990 to 2001, the leased area grew from approximately 20%
to 40%, while the biomass of mussels increased by over 300%. This corresponds to an atypical
scenario and is not considered entirely representative of other bays or other types of shellfish
production in the region. Tracadie Bay has thus become a focal point for research on the
negative environmental effects of shellfish aquaculture. However, it remains unclear as to the
net effects of the culture on the overall productivity of the bay even in these circumstances.
Miron et al. (2005) found that the absence of a strong relationship between husbandry practices
and the studied benthic parameters might be related to the oceanographic characteristics and
land-based activities associated with the water system rather than direct and cumulative effects
of mussel culture. Nonetheless, the NAP highlighted a series of concerns with regards to bivalve
aquaculture in general which are useful in this analysis. The reader may also refer to the
documents listed above for more information on benthic and water column effects.
Potential effects can be linked to the presence of oysters and the presence of structures in
the water. In the particular case of oyster aquaculture, one must also understand the functional
effects of natural oyster populations in an attempt to understand their role in aquaculture
operations. Interactions in the coastal zone between farmed bivalves and other organisms are
highly complex. Net habitat effects of bivalve aquaculture are difficult to disentangle from effects
of other anthropogenic activities (McKindsey et al. 2006a). In addition, net pathways of effects
on the environment can be both negative and positive. Figures 4 and 5 represent simplified
views of some of the complex ecological interactions that can occur in relation to bivalve
aquaculture. The scientific literature indicates a variety of levels of effects of bivalve farming
activities on the many compartments of estuarine ecosystems.
Figure 4 - Conceptual diagram of the ecosystem effects of suspension-feeding bivalves. Solid
lines indicate transfer of materials; dashed lines indicate diffusion of materials; dotted lines
indicate microbially mediated reactions (Vandermeulen 2006 from Newell 2004).
Figure 5 - Potential pathways of effects from mussel culture systems; (FAO 2006)
4.1.2 Potential sources
Potential sources of effects that can be expected from shellfish aquaculture have been
identified by ICES (2004) and only the effects relevant to fish and fish habitat are summarized in
the table below (Table 3).
4.2 Exposure characterization
4.2.1 Adversity of exposure and effects
DFO used the lists of pathways of effects and endpoints of concerns to scope potential
interactions between oyster aquaculture and Valued Ecosystem Components (VECs). A
compilation of mitigation measures currently requested of the industry to protect fish habitat was
done and applied in the analysis of effects (Table 4). The information provided by the NAP,
scientific literature, and monitoring results was also used in the evaluation of the potential
residual negative effects to fish habitat.
Table 3 - Summary of steps in bivalve aquaculture and their potential to influence fish habitat.
Based on ICES 2004 and adapted to N.B. water column oyster aquaculture.
1. Seed collection
a. artificial collectors
i. removal of juveniles from wild population of target species
ii. increasing recruitment success of oysters or other species
iii. alteration of the hydrodynamic regime
iv. acting as fish attraction device (FAD)
2. Grow-out
a. effects common to all techniques
i. organic enrichment of seafloor
ii. alteration of hydrodynamic regime (current speed, turbulence)
iii. food web effects: competition with other filter feeders, increasing recycling speed of nutrients
iv. providing food for predators of shellfish
v. control of predators and pests
vi. acting as artificial reef or FAD (attraction/displacement or enhancement of animals)
b. artificial structures (trestles, poles, rafts, longlines)
i. risk of attraction of birds
ii. risk of damage to eelgrass
3. Harvesting
a. effects common to all techniques
i. removal of biomass/nutrients
ii. removal of non-target species
iii. competition with predators
b. collection of off-bottom structures
i. risk of trampling of substrate and vegetation
4. Processing
a. effects common to all techniques
i. discard of epibionts
ii. discard of shells
Table 4 - Review of potential ecological concerns of water column oyster aquaculture.
Physical structures can
modify the hydrodynamic
patterns of water
movements by impeding or
altering water flow.
Physical structures can
change flow patterns and
increase sedimentation
under the structures.
Physical structures may
become obstacles for the
movement or reproduction
of organisms.
Site infrastructure is required to be aligned with dominant
currents to minimize impacts on water flows.
Minimal spacing recommended between structures of 3
m (industry currently spaces structure 7-10 m apart)
NWPA prohibits works in navigation channels.
Structure is considered permeable to fish and marine
mammals, no leader, net or entrapment mechanism that
could impede migration or organism movement.
No leader, lures, nets or other obstacles that could
impede movement, cause entanglement or attract
Changes in
Overwintering of physical
structures may affect
benthic fauna or flora.
Minimal concern as bags is typically overwintered during
the period of dormancy for most organisms.
Overwintering is generally conducted in deeper waters
where presence of flora is limited.
Re-suspension is done as early as possible after ice-out
to reduce losses.
Physical structures in the
water column may displace
certain organisms from the
footprint of the structure.
Addition of
structure in
the water
affecting species
Physical structures in the
water column create habitat
for organisms by providing a
substrate similar to the
effect of an artificial reef.
period depends
on local
methods and
In water column oyster aquaculture, the footprint which
can exclude organisms from an area is considered minor.
Oysters not available to predation within grow-out bags.
No lures or bait that could attract predators or
scavengers. Oysters not within diet of large marine
predators, such as seals.
Presence of epibionts on or falling off structures may
attract crustaceans, fish and birds.
Structures provide a hard
substrate for opportunistic
organisms or also for
colonizing organisms which
can serve as food for fish
and invertebrates.
Preliminary studies suggest that species diversity near
structures appears to be maintained although the species
composition may be altered.
Proponent has to select its site, deploy its structure and
adopt appropriate husbandry practices to minimize
colonization of other organisms.
Structures may affect
aquatic Species At Risk Act
No species currently listed in N.B. estuaries.
Potential risk of spatio-temporal interaction between
water column oyster aquaculture and aquatic SAR is not
significant given the spatial area where culture occurs.
Changes in light
Physical structures in the
water column may reduce
the light availability to flora
(i.e. eelgrass) directly under
the structures.
Siting of off-bottom aquaculture in eelgrass-free areas.
Minimal spacing of off-bottom aquaculture works at
minimum of 3 m, not to exceed 50% coverage of the site.
(industry currently spaces structure 7-10 m apart)
Suspended aquaculture is to be anchored to allow
swaying with each tidal cycle and to avoid continuous
shading of the same area of eelgrass.
Structures are to be designed and installed to maximize
opening to increase light penetration.
The footprint of structures on the benthos is small.
The oysters maintained in
water column aquaculture
may reproduce with wild
populations of oysters.
Not a concern given that the oysters are recruited yearly
from wild sources and not from hatcheries.
Addition of
filter feeding
Changes in
The addition of oysters may
cause a competition for
space with other organisms.
Not expected to be an issue given that oysters are held in
the artificial structures in the water column which create
additional space.
The addition of filter feeding
bivalves in the water column
may cause removal of eggs
and larvae of fish and
benthic organisms.
during egg and
larval stages –
within size
preference for
Not expected to be an issue given that C. virginica is the
native species of oyster and population interactions with
that species are expected to be similar in aquaculture as
they are under natural conditions.
Demonstrated preference by oysters for
microzooplankton as opposed to mesozooplankton.
Narrow range of opportunity if within immediate vicinity of
feeding current vs. total surface of estuaries.
Adaptation mechanisms within bivalve populations to
limit egg and larval predation of con-specifics.
Observed presence of higher diversity of species within
natural oyster beds (including other bivalves).
The addition of oysters to
the water column may
attract predators.
Seasonal Oysters are protected within the grow-out bags, except
for a limited time while on collectors.
Fouling organism fall-off from growing structure may add
food to benthos.
Additional gametes and larvae may contribute to food
No documented evidence of large predators near these
Not a preferred food-source for large predators.
Changes in
The additional biomass of
filter feeding bivalves to the
water column may cause a
depletion of plankton.
Not expected to be an issue given that C. virginica is the
native species of oyster and population interactions with
that species are expected to be similar in aquaculture as
they are under natural conditions.
Current densities are lower than historical densities
found in natural populations throughout the region.
Changes in water
The addition of filter feeding
bivalves to the water column
may remove significant
quantities of particles from
the water column that can
reduce turbidity.
This effect is largely considered to be beneficial by
reducing turbidity, thus favouring the growth of aquatic
Changes in
nutrient cycles
The addition of filter feeding
bivalves to the water column
may play a significant role in
recycling nutrient and
benthic/pelagic coupling.
This effect is largely considered to be beneficial by
removing excess nutrients through bivalve feeding as well
as harvesting.
Changes in
Biodeposition from faeces
and pseudofaeces may
increase sedimentation and
enrich the benthos which
could affect benthic
geochemistry and
Not expected to be an issue under current stocking
oyster densities and given seasonal nature of operations.
Bays where water column oyster aquaculture sites occur in
N.B. are characterised as dynamic shallow water systems
with frequent resuspension of upper layers of sediment by
wind, wave, tides, storm-events and ice-scour which likely
reduce the effect of biodeposition.
Changes caused
by equipment
Equipment installation and
regular maintenance
activities at the site may
temporarily increase
installation and
Access to the intertidal zone by motor vehicles other than
boats is prohibited under provincial regulations, unless
operating such vehicle on ice or frozen ground that is
completely covered by snow.
May cause physical damage
to the eelgrass.
Anchors are to be sized and installed to minimize
dragging, preferably during winter (eelgrass dormant
Trampling, anchoring in eelgrass, are to be minimized.
Discard of
Discards of epibionts during
maintenance may be
deposited to the benthos.
Sporadic during
Air-drying of the equipment through bag turning is the
recommended method of removal in the aquatic
Disposal and recycling of waste on land is controlled by
provincial and municipal regulations
Discard of shells Discards of shells during
maintenance may be
deposited to the benthos.
Sporadic during
Not expected to be a significant issue, discouraged by
industry to prevent spread of boring sponge (Cliona celata)
Incidental loss of small quantities is considered positive
for habitat creation
Use of artificial
or chemicals
Potential to release
undesirable compound into
the environment during
production or cleaning
Bivalve aquaculture does not require the use of artificial
food, pharmaceuticals or chemicals for production
Air drying is the typical method for cleaning equipment in
the aquatic environment. Pressure washing with water is
also used although less frequently. These methods do not
require chemical cleaning agents.
Use of lime bath to remove predators on collectors is
4.2.2 Scale and intensity of exposure
Concerns with regards to the adverse effects of bivalve aquaculture appear to be linked to
the scale and intensity of aquaculture rather than the type of culture or infrastructure used
(McKindsey et al. 2006b). In aquaculture, the scale and intensity is typically related to the
rearing density of the animals (numbers per area) and to the extent of the activity (area
occupied) (i.e. the level of exposure). Exposure is a function of sources, distribution and co-
occurrence in space and time between an effect and the receiving environment. The following
sections attempt to characterize the scale and intensity of oyster aquaculture in the sGSL. Oyster production in the Maritimes
It is difficult to obtain precise landing values from oyster aquaculture in the Maritimes
because of the way statistics on oyster production are collected and estimated. For instance,
DFO keeps records of oyster purchases, as reported on sales slips, including data on both
commercial wild-harvested and aquacultured oyster statistics and it is not currently possible to
disentangle the respective proportion of cultured versus fished oyster from the values reported.
The Province of N.B. estimates aquaculture production based on an assessment of the
number of oyster growing bags in use. In 2004, for example, the Province estimated that
165,000 oyster bags were in production, with an average of 500 oysters per bag, which would
have signified approximately 82.5 million oysters (Government of New Brunswick 2004). Only
one fourth of these would have been available for harvest (production time of 4 years), which
would amount to 20.6 million harvestable oysters (approximate size of 60 mm @ 39.10g/oyster
for an approximate total of 805t) (Government of New Brunswick 2004). Robichaud
(unpublished) conducted an audit of oyster aquaculture leases in N.B. in 2006 and arrived at a
slightly lower estimate of approximately 140,000 bags.
A comprehensive survey (interviews, boat and aerial photography) of oysters under
production in N.B. concluded that between 990 and 1,249 tonnes of oysters (all sizes included)
were under cultivation in 2005 (Comeau et al. 2006). The discrepancy in production estimates
between the three main sources of information (producers, government officials and sales slips)
illustrates some of the difficulty in quantifying actual production. Comeau et al. (2006) estimated
the actual production of marketable oysters in 2005 to have been 679 t from aquaculture and
75 t from commercial harvesting, which puts the estimated total landings at 754 t.
26 Scale of oyster aquaculture production
According to Morse (1971) interest in oyster farming, characterized by an expansion in the
number of leases and the development of seed production facilities and assistance programs,
began in earnest in the Maritimes in the 1940’s. Twenty years later, in 1966, it was estimated
that 87% of the total landings of oysters could be attributed to the public fishery and 13% from
public lease production.
Attempts have been made to project future landings by Unic Marketing which estimated
that the future contribution of aquaculture would gradually begin to increase and that it would
equal the contribution from the wild fishery by 2010 (Unic Marketing Group Ltd 2003). However,
based on the numbers above, it appears that these predictions have failed to materialize and
that aquaculture production remains below expectations. Landings from aquaculture production
may only be gradually replacing commercial landings, perhaps because natural oyster reefs
continue to be depleted (C. Noris, personal communication) and/or the industry may not be
expanding as rapidly as initially predicted.
4.2.3 Relative intensity of aquaculture production
The intensity of aquaculture production has been equated with densities of bivalves under
production for a specific surface area, or annual yield. Moreover, the culture intensity and yields
speak in part to the concept of carrying capacity.
Comeau et al. (2006) calculated that average densities of oysters grown in N.B. were
seven times lower than densities used in Normandy, France. The biomass of oysters
(0.23 kg/m2 of leased area) in N.B. by comparison to mussels or with oysters cultured in other
areas in the world (10 – 85 kg/m2) is considered to represent a low intensity production (Comeau
et al. 2006). In Spain’s Rias Bajas, one raft (average 19 x 16m) is estimated to produce 50
metric tons, or 164 kg/m2 (Tenore et al. 1982). This is one of the highest reported protein yields
per unit area and is only possible given the nutrient-rich upwelling conditions and high primary
productivity observed in this region. To illustrate the range of densities used in oyster
aquaculture, the following table (Table 5) shows oyster densities reported in the literature, along
with reported environmental effects. By comparison to the scale and intensity of these
operations, oyster aquaculture densities used in the Maritime Provinces, which are among the
lowest described in the literature, constitute a low-intensity culture situation.
The comparison of yields and reported effects also provides some indications of
thresholds of exploitation, as well as site-specific environmental conditions, that can occur and in
which detectable and significant negative impacts can be observed. We are unaware of any
study which can demonstrate significant adverse effects of bivalve culture at the densities
observed in New Brunswick water column oyster aquaculture.
It is also interesting to note that the transition to off-bottom culture resulted in an actual
reduction of stocking densities of oysters compared to on-bottom operations and natural oyster
reefs. Moreover, oyster densities in natural reefs are estimated to have been 17 to 530 times
greater than those currently measured in aquaculture (Comeau et al. 2006). Oysters in natural
and healthy oyster reefs (Table 6) occur at densities in excess of hundreds of oysters/m2 (500 –
4,000 oysters/m2, roughly equivalent to 25 to 55 kg/m2) (DeAlteris 1988; Paynter 2002; Harris
Table 5 - Yields of oysters produced in aquaculture, from temperate ecosystems, converted when applicable to a standard equivalent
of metric tonnes per hectare per year (McKinnon et al. 2003)
Reported environmental effects Species Region,
t ha-1 yr-1
Benthic infauna / epifauna Organic / inorganic
Redox / sulphides
C. gigas Tasmania,
20 Longlines No significant differences in
benthic infauna
No significant trends
in organic carbon
along farm transects
No negative redox
measurements found
beneath farms
(Crawford et
al. 2003)
C. gigas River Exe,
Trestles Decreased abundance of
macrofauna (half) restricted to
sedimentation rate,
increased organic
content (footprint)
Reduction in depth of
oxygenated layer
(Nugues et al.
C. gigas Arcachon
13 Tables Increase in meiofauna
abundance (3-4 times) and
decreased macrofaunal
abundance (half)
Elevated organic
carbon levels
Elevated oxygen
demand and anoxic
(Castel et al.
C. gigas Thau
10 Rafts,
(Chapelle et
al. 2000)
C. gigas New
8 Racks No marked trend in
macrofauna species richness,
species composition and
dominance patterns
More elevated
directly under racks
No evidence of highly
enriched conditions
(Forrest &
Creese 2006)
C. gigas B. C.
4 http://www.agf
C. virginica NB
4 Tables Macrofauna biomass,
abundance and number of
species higher or similar
No organic
Seasonal variations but
no significant differences
between control and
culture sites
(Mallet et al.
C. virginica NB
2 Longlines (Comeau et
al. 2006)
Table 6 - Documented biomass of oysters and macrofauna at natural oyster reefs
Author Location Oyster
(approx # ·m-2)
No. species
(# · m-2)*
(g · m-2)**
Dame et al. 1984;
Dame 1979
1,000 – 2,000 37 2,476-4,077 214
Bahr & Lanier
Georgia 4,000 6+ 42 38,000 705
Lehman 1974
cited in Bahr and
Lanier 1981
Florida 3,800 All
31 6,200 253
DeAlteris 1988 Virginia 10 -1,000 5-7
Harris 2003 Chesapeake
500 -1,000 Spat
Milewski &
Chapman 2002 Caraquet
67 - 84 All
3 - 14 32 - 216
ibid Miramichi
16 - 164 All
15 - 25 360 – 2,572
ibid Cocagne,
35 - 379 All
18 - 27 440 – 2,848
ibid Bouctouche,
60 – 1,603 All
19 - 29 504 – 6,448
Sephton & Bryan
250 - 420
* Min-Max reported, **soft tissue wet weight
4.2.4 Potential co-occurrence
Another element to consider is the potential for co-occurrence between the activity and the
environment (i.e. competition for space). A common proxy to help assess the potential impact of
aquaculture operations is to estimate the proportion of the total bay surface which is occupied by
leases. Shellfish aquaculture lease sizes in the Maritime Provinces are mostly small, averages
range from 3.51 ha to 15.71 ha (Table 7), but some leases can be considerably larger. In N.B.
approximately 60% of oyster leases are smaller than 4 ha (Figure 6). Of the total number of
lease sites not registered as vacant, an unknown number of sites essentially lie fallow with little
or no effective activity (C. Noris, pers. com.).
Table 7 - Number and surface area of active leases issued by area in the southern Gulf of St.
Lawrence, 2001-2002.
Leases Total surface area
of leases
Average surface
area per lease
AREA Number Hectares Hectares
Prince Edward Island 776 2,721 3.51
Eastern New Brunswick 624 2,513 4.03
Gulf Nova Scotia 33 518 15.71
TOTAL 1,433 5,752 4.01
Includes all estuaries in N.B. where oyster aquaculture is conducted, except Baie des Chaleurs.
<2 2+ 4+ 6+ 8+ 10+ 12+ 14+ 16+ 18+ 20+ 22+ 24+ >26
Number of leases
Lease surface area (hectares)
Active Vacant
Figure 6 - Surface areas covered by active and vacant oyster leases in N.B. (data from NBDAA,
2007; n=658)
A GIS analysis of the area of leases area to total estuarine waters surface area shows that
less than 5% of the surface of N.B. estuaries is defined as lease area, for all techniques included
(data from NBDAA). Within these leases, the effective coverage or actual footprint of the
aquaculture gear is limited by several factors (e.g. vacant space, navigation channels, unsuitable
water depths in the lease, etc.). Thus the effective coverage is calculated as follows:
For a lease with a total surface area of 1 hectare: 100 m X 100 m = 10,000 m2 (x)
Longlines -10 per hectare
Total surface area occupied by longlines = (60 m X 2.0 m) X 10 = 1,200 m2 (y)
Percentage of lease covered by gear = ( y ÷ x ) X 100 = 12%
Cages -240 per hectare
Total surface area occupied by cages = (2 m2 X 240) = 480 m2 (y)
Percentage of lease covered by gear = ( y ÷ x ) X 100 = 4.8%
Therefore the aquaculture gear typically occupies between 5 to 15% of the surface area of
a lease; or less than 1% of most bays. The footprint associated to the gear should likely be
considered more representative of the affected area, in terms of fish habitat, rather than the total
surface of the lease of which much of the lease area is not utilized.
4.3 Sensitivity of fish habitat
4.3.1 Characteristics of estuaries in N.B.
The biological composition of fish habitats in estuaries is generally found to be dynamic,
constantly evolving and responsive to varying environmental gradients (Attrill & Rundle 2002;
Attrill & Power 2004). In general, estuaries in eastern N.B. share similar characteristics. They are
partially enclosed and protected from the open sea by systems of dunes and barrier islands. The
different combinations of freshwater and saltwater inflow, precipitation, temperature, tidal range,
dissolved oxygen, sediments loading and wave action lead to the development of a range of
connected fish habitats within the estuary. Spatial delimitation between these various fish
habitats is defined by nuances in physical, chemical and biological characteristics. These in turn
affect the sediment characteristics, nutrient and oxygen availability, desiccation and immersion
profiles, water temperature and salinity, etc. Current flow and wave action generally determine
the sorting of sands, gravels and silts and the formation of mud and sand flat areas, salt
marshes, sand or gravel beaches, shallow inlets and bays.
Eastern N.B. estuaries are generally shallow; as a result, the seasonal range in surface
water temperature is among the highest in Atlantic Canada. Typically, water temperatures will
reach 16-22°C in the summer; and -1°C to 5°C in the winter (DFO 1996). Seasonal ice generally
covers these estuaries between December and March. Hence, overlap of boreal and temperate
fish species can be observed with a north-south gradient in species composition.
The sGSL is considered a biologically diverse region and an important spawning ground
and nursery area for a number of commercially important fish species (DFO 2001). N.B.’s
estuaries contribute significantly to the overall ecological richness and productivity of this region.
Two characteristics of this production is the large seasonal increase in plankton and the variety
and abundance of larval fish and invertebrate species (DFO 2001).
Intertidal and subtidal areas support pelagic, benthic and burrowing communities of
organisms. The location and composition of these communities is determined mainly by the suite
of physico-chemical variables. Plant and animal communities depend on ambient conditions for
providing nutrients, oxygen and carbon supplies. Another factor influencing the nature of these
communities is the bathymetry or depth profile and the degree of wave action. Wave action,
particularly during storms, ice-scouring (Robertson and Mann 1984) and exposure may in turn
affect intertidal communities. This is likely to be more observable in shallow waters and can
result in varying levels of sediment and biota transport and turbidity.
The salinity structure in estuaries is primarily determined by the seasonal freshwater
discharge. Attrill and Rundle (2002) suggested that estuarine compartments are mainly defined
by salinity which is a primary factor affecting the distribution of estuarine communities. Stable
groupings of species tend to follow thermal or salinity boundaries (Attrill & Rundle 2002). In
eastern N.B., the salinity gradient typically increases from low levels near the inshore freshwater
source to higher levels where the estuary opens into marine conditions of the sGSL. Salinity
stratification may occur in deeper regions of the estuary during certain seasons, but typically the
shallow periphery of the estuary is homogenous because of active wave and current mixing.
Relatively stable salinities are found near the freshwater tributaries and the estuary mouth.
4.3.2 Sensitivity characterization
The principal distinction between natural oyster populations and oyster aquaculture with
regards to its influence on the sensitivity of fish habitat is tied to the presence of physical
structures which have the potential to have localized affects on the physical characteristics of
estuaries, such as wave and tidal currents, turbidity and sediment mixing. When compared to
storm events, the influence of physical structures in the water appears minimal, and unlikely to
affect the sensitivity of fish habitat. Stochastic natural events are more likely to have significant
and widespread impacts on estuarine plants and animal communities than aquaculture activities
(Mallet et al. 2006). These natural disturbances are believed to be necessary conditions for the
maintenance of stable biotic communities, since they promote the redistribution of resources
within the ecosystem (Rykiel 1985).
As seen above, variability is inherent to the physico-chemical and biological characteristics
of estuaries. Estuarine plant and animal communities need to be able to endure significant
seasonal and geographic variability in conditions. They have to be well adapted to survive the
physical stresses imposed by these extremes.
4.3.3 Sensitivity of fish species
Many species in the sGSL region are dependent on estuaries for at least a phase of their
life history as feeding, nursery, migration and/or spawning habitat. They are thus potentially
vulnerable to impacts from habitat alteration. Particularly susceptible are species or species
groups that require estuaries or freshwater tributaries as primary larval or post-larval habitat. In
the N.B. region, these species include anadromous fish such as striped bass, blueback herring,
alewife, American shad, sturgeons, rainbow smelt, Atlantic tomcod and winter flounder.
Other commercial fish species found in estuaries include various species of bivalves, such
as mussels, quahogs and clams and crustaceans, such as rock crab and lobster. The effect of
water column oyster aquaculture on these fish species is generally considered minimal as the
structures do not impede fish movement. In addition, Powers et al. (2007) and DeAlteris (2004)
demonstrate that aquaculture structures can provide biogenically structured habitats that
function as nursery and feeding habitats for juvenile fishes and mobile invertebrates.
4.3.4 Sensitivity of submerged aquatic vegetation
In N.B. the fish habitat most likely to co-occur and to be affected by oyster aquaculture is
eelgrass (Zostera marina) beds. Zostera is considered important in maintaining desirable
ecological properties of estuaries due to photosynthetic activity, its role in biomass accumulation
and in nutrient cycling. In addition, eelgrass plays a important role as a nursery habitat for a
variety of fish and invertebrate species (Locke & Hanson 2004) such as juvenile white hake and
small cunners (Joseph-Haché et al. 2006).
Several factors are known to affect potential eelgrass growth and recovery (UK Marine
special areas of conservation 2006), such as: the removal of habitat; the creation of unstable
substrata; the fragmentation and destabilization of Zostera beds caused by factors such as
changes to coastal processes; physical damage or stochastic weather events; reduced rhizome
growth and seed production; reduced light penetration caused by increased turbidity, changes in
salinity, pollution or epiphyte smothering; nutrient enrichment; declines in epiphyte grazer
populations; unusual increases in waterfowl grazing pressure; non-native macrophyte species,
exposure to extreme temperatures, which may increase the susceptibility to disease.
Worldwide, two of the most important threats to submerged aquatic vegetation are disease
and anthropogenically induced eutrophication (Short et al. 2001). Nutrient pollution effects on
eelgrass and nitrogen loading from a variety of sources such as agriculture run-off, sewage, and
fish plants are described to varying degrees in N.B. estuaries (Conservation Council of New
Brunswick 2004, Lozte et al. 2004).
In oyster aquaculture, eelgrass may be affected principally by incidental removal (mooring,
boat wash, trampling, etc.), by biodeposition or by shading. This effect is variable in spatial
distribution and severity and appears tied to the equipment’s footprint. Table 8 describes some
impacts of different activities on Zostera populations and observations about its resilience. It
shows that in general, Zostera is not overly sensitive to changes and perturbations. Auster &
Langton (1998) observe a consistent pattern of resilience of Zostera populations in studies of the
impacts of fishing activities. Table 8 also lists pre and post impacts from a number of activities,
such as oil spill, herbicide application and wildlife grazing. Other than those cases of intense
removal of stems and meristems, effects on Zostera appear to have minimal long term impacts.
At present, rarity is generally not a concern in N.B., as Zostera meadows are ubiquitous
throughout the region and eelgrass is the dominant attached vegetation in these estuaries
(Joseph-Haché et al. 2006). There are signs, however, that cumulative human activities are
having growing impact on these meadows. Increased shoreline developments, recreational and
touristic activities are having notable physical impacts.
Globally, studies show that increased nutrient loading to estuaries can lead to eelgrass
disappearance (Hauxwell et al. 2001,Lotze et al. 2003, Cardoso et al. 2004). Locke (2005) has
observed that the above-ground biomass and percent cover of eelgrass in estuaries along the
Northumberland Strait are showing signs of decline; disturbance by the introduced green crab
and global environmental changes are mentioned as possible explanations (Locke 2005). Thom
et al. (2003) suggest that climate variations can have profound effects on eelgrass. They found
that large-scale changes climate may strongly influence eelgrass abundance that can vary by as
much as 700% annually.
Table 8 - Summary of findings on Zostera sp. recovery and sensitivity to various impacts.
Habitat Source of
effect Location Results References
Eelgrass Scallop
North Carolina Comparison of reference quadrats with treatments of 15 and 30 dredging in
hard sand and soft mud substrates within eelgrass meadows. Eelgrass biomass
was significantly greater in hard sand than soft mud sites. Increased dredging
resulted in significant reductions in eelgrass biomass and number of shoots.
Fonesca et
al. 1984 in
Auster &
Clam rake
and “clam
North Carolina Comparison of effect of two fishing methods.
Raking and “light” clam kicking treatments, biomass of seagrass was reduced
approximately 25% below reference sites but recovered within 1 year.
In “intense” clam kicking treatments, biomass of seagrass declined
approximately 65% below reference sites. Recovery did not begin until more
than 2 years after impact and biomass was still 35% below the level predicted
from controls.
Peterson et
al. 1987 in
Auster &
Clam rakes
(pea digger
and bull
North Carolina Compared impacts of two clam rake types on removal of seagrass biomass.
The bull rake removed 89% of shoots and 83% of roots and rhizomes in a
completely raked 1 m2 area. The pea digger removed 55% of shoots and 37%
of roots and rhizomes.
Peterson et
al. 1987 in
Auster &
Seagrass Trawl Western
Noted loss of Posidonia meadows due to trawling; 45% of study area. Monitored
recovery of the meadows after installing artificial reefs to stop trawling.
After 3 years plant density increased by a factor of 6.
Guillen et
al. 1994 in
Auster &
Eelgrass Recreational
Oregon Experimentally tested by raking or digging for clams in 1 m2 plots in eelgrass
meadows. After three monthly treatments, eelgrass measures of biomass,
primary production (leaf elongation), and percent cover were compared between
experimental and control (undisturbed) plots. Clam digging reduced eelgrass
cover, above-ground biomass and below-ground biomass in measurements
made 1 month after the last of three monthly treatments. 10 months after the
last clam digging treatment, differences between treatment and control were not
statistically significant.
Boese 2002
Eelgrass Physical
Danish sites Shallow eelgrass populations form characteristic landscapes with a
configuration that is highly related to the level of physical exposure; the size and
position of eelgrass beds changes substantially among years
et al. 2004
Eelgrass Experimental
San Francisco
Bay + Puget
Eelgrass was removed from experimental plots. Substantial vegetative
recolonization (64.3 -81.8%) of test plots occurred within five months of
treatment. Rapid recolonization was explained by the presence of new shoots
migrating to excavated plots and reseeding.
Fonsecal et
al. 1983
Eelgrass Mussel
Maine Aerial photography, underwater video, and eelgrass population- and shoot-
based measurements were used to quantify dragging impacts within 4 sites that
had been disturbed at different times over an approximate 7 year interval, and to
project eelgrass meadow recovery rates. Dragging had disturbed 10% of the
eelgrass cover. Dragging removed above- and belowground plant material from
the majority of the bottom in the disturbed sites. One year following dragging,
eelgrass shoot density, shoot height and total biomass of disturbed sites
averaged respectively 2 to 3%, 46 to 61% and <1% relative to the reference
sites. Substantial differences in eelgrass biomass persisted between disturbed
and reference sites up to 7 year after dragging. The pattern and rate of eelgrass
bed recovery depended strongly on initial dragging intensity; areas of relatively
light dragging with many remnant eelgrass patches (i.e. patches that were
missed by the mussel dredge) showed considerable revegetation after 1 year.
Neckles et
al. 2007
Eelgrass Canada
Maine A flock of Canada geese Branta canadensis L. over-wintered and grazed on
eelgrass for 3 months. Before Canada geese were present, eelgrass
parameters demonstrated seasonal fluctuations typical of the region. During the
grazing event, eelgrass parameters declined drastically, and biomass losses
were significant. After the event, eelgrass recruitment via sexual reproduction
was minimal, and vegetative recovery was impeded by Canada goose
consumption of the plant meristems. Unlike studies in other locations, which
show seagrass quickly rebounding from annual grazing events, eelgrass in this
location showed little recovery from grazing 1 year after the event.
Rivers &
Short 2007
Eelgrass Wasting
Eelgrass declined precipitously in the 1930s due to the pandemic wasting
disease and a destructive hurricane in 1933. Natural recovery of Z. marina,
possibly deriving from either small remnant stands or undocumented transplant
projects was significant in four northern bays, with over 7319 ha reported
through 2003 compared to 2129 ha in 1986, an average expansion rate of 305
per year. This rapid spread was likely due to seeds and seed dispersal from
recovering beds.
Orth et al.
Zostera sp. Exposure to
Diuron and
Laboratory &
Australia Zostera capricorni was exposed to 10 and 100 μg herbicide solutions for 10h.
Laboratory samples exposed to these herbicides were severely impacted during
the exposure period and most treatments did not recover fully after 4 days. In
situ samples were severely impacted by Irgarol and Diuron exposure whereas
samples recovered completely after exposure to Atrazine at the same
concentrations as the laboratory experiments.
MacInnis &
Ralph 2003
Zostera sp. Brant goose
Europe ”Wasting disease" affecting Atlantic Zostera stocks during the 1930s was at
least partly responsible for a steep decline in Brant goose population sizes on
both sides of the Atlantic. While Zostera is of outstanding importance as food for
Brant geese, the impact of the geese on Zostera stocks seems to be less
important - at many sites, the geese consume only a small amount of the
available Zostera, or, if they consume more, the seagrass can regenerate fully
until the following season.
Eelgrass Oil spill Alaska A year after the Exxon Valdez oil spill, eelgrass densities were 24% lower at
oiled sites compared to control sites. Recovery of eelgrass occurred by the
second year, with no significant differences noted between oiled and control
sites in subsequent years.
Dean &
Jewett 2001
Zostera sp. 2-4-D
The industrial herbicide 2-4-D was used to clear eelgrass from oyster grounds in
part of Baie Brulée in 1968. Surveys in 1986 showed that the area was densely
vegetated with eelgrass; eelgrass beds covered 97.7% and 46.1% of the area of
the bay in St. Simon Sud and St. Simon Nord, respectively.
Mallet pers.
Zostera sp. Oyster
California Study plots were established to test the effect of oyster line spacing distances of
1.5 ft (narrow), 2.5 ft (standard), 5 ft (wide) and 10 ft (very wide). They
examined the eelgrass, benthic infauna cores, deployed baited fish traps and
measured water quality, sedimentation, light intensity, and oyster growth. After
two years, eelgrass spatial cover and shoot density were consistently high
within the control (reference areas) and lowest within the 1.5 ft oyster line
spacing plot. Eelgrass metrics generally scaled directly with oyster density, and
the spatial cover and density of eelgrass plants within the 10 ft spacing plot
were within the range of variability observed in the reference (control) study
Rumrill &
4.4 Significance of ecological risk
The concept of significance can not be separated from the concepts of "adversity" and
"likelihood" and must be considered by taking into account the implementation of mitigation
measures (CEAA 1994). The following definitions represent guidance for the determination of
significance and were elaborated based on the CEAA and the HMP Risk assessment
Significant : A residual environmental effect is considered significant when it induces
frequent, major levels of disturbance and/or when the effects last longer than a year and
extend beyond the project boundary following the application of mitigation measures. It
is either reversible with active management over an extended term or irreversible.
Not-significant : A residual environmental effect is considered not significant when it is
infrequent, minor or negligible levels of disturbance and/or damage and when the effects
last less than a year and are contained within the project boundary following the
application of mitigation measures. An effect that is not significant is reversible with or
without short-term active management.
The significance of the ecological risks associated with water column oyster aquaculture is
based on the best current available information in the context of our understanding of the
ecosystem dynamics. The following points discuss some of the more complex concerns that are
typically raised and where ongoing research occurs in regards to water column oyster
aquaculture effects on fish and fish habitat.
4.4.1 Biodeposition
One of the principal concerns with regards to the potential negative effects of bivalve
culture is related to the increased deposition of organic matter associated with the accumulation
of faeces and pseudofaeces as well as the deposition of shells and attached epifauna from the
structures and changes to the hydrodynamics of the site. The impact of these effects on the
benthos can range from significant, in the case of intensive Asian and European culture
practices, to minimal in the case of semi- to low-intensity operations; (Chamberlain et al. 2001,
Crawford 2003, McKindsey et al. 2006a). It would therefore appear that there is a potential for
localized negative effects on the ecosystem due to increased organic loading within the footprint
of individual farms under certain conditions (e.g. heavy loading, low flushing rates, shallow water
depth, etc.).
Models can be used to predict the dispersion of biodeposits as they fall from the
aquaculture works and assess the extent of the activity’s footprint. Chamberlain et al. (2006)
show that in shallow depth sites, such as in water column oyster aquaculture, deposits are
expected to fall largely under the equipment. They also show that particle flux is correlated to
the stocking density of the cultured species and also that resuspension and mixing of these
particles are likely to occur in shallow systems. Thus, the impact of biodeposition depends
largely on the density of shellfish present at the site and extent to which water exchange will
disperse of the deposits.
In the case of water column oyster aquaculture, studies on sedimentation rates in St.
Simon Bay N.B. showed that deposition rates increased at culture sites possibly from the
oysters, fouling organisms and hydrodynamic effects of the equipment (Mallet et al. 2006).
However, the mean organic content of the sediment deposited at the Oyster Table site (20.2%)
was not significantly different from the Floating Bag (20.8%) or the Reference sites (21.8%)
(Mallet et al. 2006). The authors suggested that the lack of enrichment of the sediments
indicated that the organic matter in the biodeposits was not being incorporated into the
sediments and was either washed away and/or rapidly processed by the benthic community.
When organic enrichment occurs, as seen in intense finfish aquaculture, it can cause
alterations in the benthic community; reducing species diversity and richness as the impact
accentuates (Pearson and Rosenberg 1978; Rosenberg 2001). Mallet et al. (2006) concluded
that, the number of species and macrofaunal abundance was similar at the culture and the
reference sites, and there was no evidence of opportunistic species typically associated to highly
disturbed areas.
The use of Eh/Sulphide analyses of the sediments was developed for finfish aquaculture
as a quantitatively index of organic enrichment and the formation of anoxic sediments and levels
were correlated with the composition of the benthic community (Wildish et al. 2001). This
technique has been applied elsewhere but to date no significant impact was detected for the
analyses of the sediments under oyster sites (Mallet et al. 2006) in Baie St. Simon N.B., one of
the most intensively cultured bays in the Province. Mallet et al. (2006) found that Eh/Sulphide
levels at oyster sites were not significantly different from reference sites. Additionally, as part of
an MOU with the N.B. provincial government, the NBDAA has initiated surveys to measure
Eh/Sulphide levels in and around oyster aquaculture sites. In 2006, sites within two bays which
are considered important oyster aquaculture areas were assessed on and off leases. They
found that in Baie St. Simon and in Richibucto, levels of sulphides in the sediments averaged
314 µM and 159 µM, respectively (data from NBDAA). The maximum levels observed 1410 µM
and 1165 µM for Baie St. Simon and Richibucto respectively, occurred outside the leases in the
deeper areas of the navigation channels (data from NBDAA). Hypoxic conditions in the
sediments occur at sulphide values of 1,500-3,000 µM while anoxic conditions correspond with
levels of 3,000-6,000 µM or more (e.g. Wildish et al. 2001, Holmer et al. 2005).
Therefore, there is no indication to date of significant or adverse effects associated with
the increase in biodeposition under water column oyster aquaculture sites in N.B.
4.4.2 Carrying capacity
There is concern over to the potential effect of increasing the oyster biomass on the
carrying capacity of estuaries. As shown in section 4.2, the intensity observed in water column
oyster aquaculture in N.B. differs significantly from other regions in the world.
Several attempts have been made internationally to determine the carrying capacity of
estuaries for shellfish production. One of the main obstacles is the lack of clarity in the definition
of carrying capacity. For shellfish culture, McKindsey et al. (2006b) favour the use of “ecological
carrying capacity” which represents the point where the stocking density on the farm is high
enough that it can cause unacceptable environmental impacts. Typically, the carrying capacity
for shellfish is based on the biomass which can be supported in a given bay in terms of food,
habitat, water quality and other necessary parameters. Research in this area has been limited
by the complexity of seasonal and size related changes in energy requirements of shellfish,
seasonal changes in productivity, trophic characteristics of estuarine communities and
hydrodynamics of many areas. Various problems have been reported in the literature about
models used to determine carrying capacity and their requirement for long term environmental
data collection. Newell (2007) highlights the shortcomings of current models in accurately
representing conditions observed in shellfish aquaculture and lists the steps required to improve
these efforts; including a better account for ecosystem functions provided by bivalves which
have desirable (e.g. economic, environmental remediation and nutrient trading scheme)
outcomes. In particular, these models need to take into consideration the cumulative effects of
neighbouring human activities (e.g. nutrient run-off, sedimentation, etc.) (ICES 2003).
The carrying capacity of a given system is not at a static or unchanging level. Seasonal
changes in temperature, food supply or other factors can affect the capacity of a bay or estuary
to support the organisms within it (Carver and Mallet 1990). Bivalve culture is strongly
influenced be the quantity of food (i.e. plankton and organic particles) which is available in the
water column. The Aquatic Ecosystem Section of DFO in the Gulf region initiated the Shellfish
Monitoring Network (DFO 2007) ( in order
to examine spatial and temporal variations in shellfish productivity using standardized cage
systems in bays with oyster or mussel culture in the sGSL. For example, differences in growth
rates of bivalves in different bays between years are often more important than differences
between bays despite varying intensities of bivalve culture within the bays. This suggests that
productivity is linked more strongly to broad annual changes in nutrient inputs, plankton blooms
or temperatures than to grower interventions within a given bay. This monitoring of shellfish
productivity is ongoing and will continue to provide a baseline of shellfish growth so as to provide
an indication of ecosystem effects if changes outside of the natural variability are observed.
Given historical levels of natural oysters within N.B. estuaries (see section 5.2 Historical
state of oyster populations) as well as the comparisons with bivalve production in other regions
of the world, it appears that the ecological carrying capacity of these systems is not likely to be
adversely affected by the anticipated level of water column oyster aquaculture.
4.4.3 Nutrients
The effect of nutrient releases such as nitrogen and phosphorous from farmed oysters in
the form of faeces and pseudofaeces is generally considered of lower importance compared to
the regional inflow of nutrients in open water masses (Folke & Kautsky 1989, Kirby & Miller
2005, Ferreira et al. 2007). Generally, the excretions that oysters do produce are thought to be
rapidly assimilated by plankton in the water column (Pietros and Rice 2003). Shellfish in culture
consume ambient plankton and are not artificially fed. Thus they do not add nutrients but rather
can alter the nutrient dynamics and concentrate nutrients in the farm’s immediate surroundings
(McKindsey et al. 2006a). This concentration of nutrients can be difficult to assess in the water
column and explains why appreciable efforts are made to study benthic enrichment and
biodeposition, as discussed above.
Unlike finfish aquaculture, where one of the main ecosystem stressors is related to the
addition of nutrients, chemicals and pharmaceuticals in the form of fish food, bivalve aquaculture
represents an extractive activity, by which the bivalves filter food out of the water column and
these nutrients are removed from the ecosystem entirely at harvest. Sarà (2006) conducted a
meta-analysis on the ecological effects of aquaculture on nutrients by comparing shrimp, fish,
bivalve culture as well as polyculture. The author concluded that the effect of aquaculture on
nutrients was highest in freshwater and lowest in marine water. Moreover, the author found that
bivalves appeared to have no significant influence on the dissolved nutrients and their “mean
size of effect” was negative (-0.03) unlike the positive values seen in shrimp (+0.71), fish (+1.10)
and polyculture (+1.80) (Sarà 2006).
That said, although oysters are known to have been highly abundant historically, the role
of shellfish aquaculture in influencing the nutrient dynamics in estuaries, as well as in selective
grazing of plankton, remains an ongoing research topic.
4.4.4 Submerged aquatic vegetation
Another common concern relates to the potential damage to submerged aquatic
vegetation which is considered valuable habitat for several fish species (e.g. Chambers et al.
1999; Joseph et al. 2006; Vandermeulen et al. 2006 ). Marine plants such as eelgrass are
considered critical habitat in many parts of the world because they serve important ecological
functions, are often considered rare, and thus are often the subject of monitoring programs
(Short et al. 2001). It is important for many fish and invertebrates and contributes to the
ecological richness of the region. In N.B. estuaries, the eelgrass (Zostera marina) is considered
abundant in many bays. Surveys have shown that eelgrass beds can represent appreciable
portions of N.B. estuaries (SEnPAq 1990ab). For example, in Baie St. Simon Sud and in
Richibucto Bay 98% and 78% of the surface area of the bays, respectively, was covered by
eelgrass beds; these values do not exclude sediment types unsuitable for eelgrass. The
SEnPAq (1990ab) study is currently being used as a baseline with which to compare eelgrass
distribution. A DFO working group is presently assessing eelgrass as a potential indicator for
evaluating bay health in N.B. in collaboration with Environment Canada, Parks Canada and
Eutrophication remains the main concern to eelgrass productivity and is recognized as a
threat by increasing epiphytes on the leaves, and reducing water clarity which cause shifts in the
primary productivity from benthic vegetation towards phytoplankton. It is clear from the scientific
literature that shellfish filtration plays a critical role in improving water clarity which increases
light availability and enhances bioavailability of nutrients and thereby stimulating eelgrass growth
(e.g. Kennedy V.S. 1996; Newell & Koch 2004; Kirby & Miller 2005; Newell et al. 2005). This
positive interaction can apparently be reduced in certain highly eutrophic settings such as in the
Thau Lagoon in France (e.g. DeCasabianca et al. 1997 and 2003).
Other concerns may relate to physical disruptions as eelgrass can be dislodged by
aquaculture activities such as trampling, anchoring, and powerboat wash. Past practices,
whereby oyster culture was conducted by partial removing of eelgrass in order to facilitate
removal of oysters and increase water flow, are no longer carried out. Vandermeulen et al.
(2006) state that the preservation of habitat can be achieved by ensuring adequate spacing
between lines and by minimizing physical impacts. Rumrill and Poulton (2004) found that oyster
aquaculture gear placed line-spacing at 3m exhibited eelgrass metrics that fell within the range
of variation observed in a series of reference areas while significant impacts occurred at smaller
line spacing. The current space left for boat navigation (typically >7 m) is typically greater than
the (>3 m) minimum spacing which was recommended by the NAP (Vandermeulen et al. 2006).
Dumbauld (2005 cited in Vandermeulen et al. 2006) states that eelgrass can recover in 1-2
years if left undisturbed.
Stephan et al. (2000) compiled results on the effects of impacts of fishing gear (i.e.
dredging, trawling, raking, etc.) on submerged aquatic vegetation and qualified the “injury
recovery potential” of eelgrass Zostera marina as “moderate” in comparison to ten other species
marine vegetation. Peterson et al. (1987) evaluated the effect of different intensities of
mechanical harvesting of clams (Mercenaria mercenaria) including the “clam-kicking” technique
which involves directing the propeller wash downward with sufficient force into the sediment to
displace the sediments thus exposing the clams for easy collection with a trawl. They found that
“intense kicking” had significant effects in reducing eelgrass biomass while “light-kicking” and
raking had much lower impacts. Eelgrass in the “light-kicking” and raking treatments recovered
to the level of the controls within 1-year.
Based on the studies of eelgrass resilience to anthropogenic activities presented above
and natural disruptions (e.g. grazing, ice-scours, annual variability with environmental
conditions), the potential effect of these physical disruptions associated to water column oyster
aquaculture is likely to affect a limited area and to be fully reversible.
4.4.5 Species interactions
Concerns with regards to species interactions typically relate to the presence of additional
oysters in the water column. Abgrall et al. (in prep.) completed a review of intra and inter-specific
interactions between the oyster and softshell clam (Mya arenaria). Although cultured and wild
population interactions, such as predation, competition, etc. are likely to occur, there is no
indication that these interactions differ significantly from those occurring between wild
populations. Oysters cultured in the sGSL are native to this region and have co-existed with
other native species; therefore they are expected to retain similar biological interactions with
existing populations.
Other concerns relate to the structures in the water column. The study of the effects of
these types of structures has evolved into a research field which refers to them as Fish
Aggregation Devices (FAD) (e.g. Castro et al. 2002). Some authors have proposed that the
aquaculture equipment itself, and other structures, may contribute to estuarine productivity by
creating a hard substrate; availability of these surface areas can limit the colonization of certain
organisms (McKindsey et al. 2006a). Passing from an essentially two-dimensional sand-mud
habitat to a three-dimensional hard surfaced habitat can dramatically alter the surface area
DeAlteris et al. (2004) conducted a study to compare the relative habitat value of
aquaculture gear (rack and bag), submerged aquatic vegetation (Zostera marina), and shallow
non-vegetated seabed. They found that the ecological value of aquaculture gear was significant
based on an assessment of resident and transient marine organism’s abundance and diversity in
the respective habitats. Aquaculture gear increased habitat complexity and supported higher
abundances of organisms than non-vegetated seabed; this was determined to be particularly
beneficial to recreational and commercial fish and invertebrate species in their early life stages.
DeAlteris et al. (2004) concluded that the relative habitat value of aquaculture gear is at least
equivalent to submerged aquatic vegetation. Powers et al. (2007) demonstrated that flora and
fauna associated to clam aquaculture gear (netting) was significant and that community structure
of mobile invertebrates and juvenile fishes utilizing leases was more similar to that of seagrass
than sandflat habitats. They found that the utilization by juvenile fishes was 3 times greater in
seagrass and 3 to 7 times greater in epibiota on mesh in clam leases than on sandflat habitat.
Similarly, a study done in the sGSL in 2006 monitored levels and types of epifauna found
on floating oyster bags (Mallet et al. in preparation). Undisturbed oyster aquaculture bags can
accumulate 500 g to 1500 g (wet weight) of epifauna (e.g. amphipods, algae, arthropods,
molluscs, etc.) per bag in one season. This can have important ramifications for the food web.
For example, the estimated abundance of the tube amphipod Jassa sp. reached over 185,000
individuals per bag in the fall. This may represent an abundant food source for small fish (e.g.
sticklebacks, silversides, cunner, etc) which appeared to be feeding on the surface of the bags
(Mallet et al. in preparation).
In addition, the epibenthic fauna community was assessed in areas of suspended bag
oyster aquaculture in three N.B. bays in 2006. Trawls were collected within leases (0 m) and at
subsequent distances of 25 m, 100 m and 500 m away from lease edge (Skinner et al. in
preparation). In general, it was found that the total organism abundance and species richness
was significantly higher at lease sites than off-lease; lease site communities were generally
dominated by shrimp species and blue mussels. The contribution of aquaculture gear to habitat
value is explained in part by the fact that oyster culture creates several compartments (hard and
soft substrata, foraging, refuge and nursery habitat) and trophic levels (primary producers, filter-
feeders, deposit-feeders) within the water column (Mazouni et al. 2001). However, opportunistic
predators such as sea stars and rock crab (Cancer irroratus), which can be abundant in mussel
aquaculture sites and seen feeding on mussel fall-off, were only observed infrequently at the
oyster aquaculture sites (Hardy, unpublished data).
4.5 Conclusion of Ecological Risk Assessment
This Ecological Risk Assessment identifies and characterizes many of the risks to fish and
fish habitat relating to water column oyster aquaculture and discusses them in the context of the
scientific literature and ecosystem dynamics. It is important to note that this assessment should
be considered by habitat managers as a starting point and be revisited as new information
becomes available.
The research priorities identified in the NAP as well as others, once completed, will further
enhance and clarify some of the uncertainties involved with this activity. Moreover, we
recognize that uncertainties exist and will continue to exist as these are complex ecosystems
and more scientific research in this field is encouraged.
It is clear that the “scale and intensity” of the shellfish aquaculture operation is the main
driver leading to potential negative effects. Culture of the native oyster in N.B. is practiced at
densities much lower than other regions in the world and the potential effects are considered
reversible and generally limited to site footprint. Based on the risk assessment matrix, our view
is that the residual “scale of negative effects” associated with water column oyster aquaculture,
as practiced in N.B., is low.
In terms of sensitivity, eelgrass beds are the principal driver in the risk matrix as they are
considered important but are ubiquitous in many N.B. bays. Eelgrass also appears to be
resilient to severe impacts, provided water quality is maintained. Eutrophication and turbidity
appear to be the main factors affecting water quality and thus eelgrass sensitivity. Ensuring
water quality should likely be the focus for eelgrass health. Because of concerns with water
quality in general, our view is that level of “sensitivity of fish and fish habitat”, based on the risk
assessment matrix, is moderate.
In our view, the potential residual negative effects associated to this activity can likely be
managed with appropriate planning and mitigation measures. Water column oyster aquaculture,
as practiced in Gulf N.B., is not considered likely to significantly harm the productive capacity or
the integrity of the fish habitat in these ecosystems. Therefore, overall based on the current
state of knowledge and the scale of water column oyster aquaculture, we conclude that the
potential residual risk for significant adverse impacts on fish and fish habitat to occur is low and
that this constitutes a low-risk activity.
This view is also consistent with a DFO’s Aquatic Ecosystem Section advice on water
column oyster aquaculture as practiced in Gulf N.B., with a broader view on the role of
aquaculture (similar to NEBA considered in the following section). They concluded that this
activity represents a low risk to cause negative effects on fish habitat based on:
the current husbandry practices (and the Code of Practice) employed by the oyster
aquaculture industry;
the relatively low biomass of oysters on an aquaculture lease;
the existence of naturally occurring reefs at densities in excess of the biomass
used in aquaculture;
the high historical landings of oysters in N.B. which suggests a high natural
carrying capacity;
the nature of shellfish as filter feeders in consuming and recycling nutrients;
the problem of increasing nutrient load of estuaries associated with human
activities and the ability of filter feeders to help mitigate these effects;
the harvesting of the shellfish on a yearly basis which can remove tonnes of
organic and inorganic matter from the bays; and
the culture of oysters over the past decades in N.B. without significant
demonstrable adverse effects.
In the above risk assessment, the potential for environmental impacts of aquaculture
works were considered, here we consider the potential remediation role that oysters can play.
The NAP concluded that bivalves in culture appear to fill many of the same ecological roles as
natural bivalve communities, a role considered generally beneficial for a number of components
of temperate estuarine ecosystems.
Although oysters in aquaculture differ from reefs in their structural form, it is useful, in the
current assessment, to consider the ecological services played by oysters. Coastal ecosystems
and estuaries dominated by bivalves exhibit complex responses that are not easily explained by
linear dynamics (Dame et al. 2002). Net environmental benefit analysis (NEBA) is an elaboration
upon the conclusions of an ecological risk assessment which considers benefits, along with
risks, which can help managers in their decisions (US Department of Energy 2003).
5.1 Historical state of oyster populations
Milewski and Chapman (2002) provided a synopsis of the history of oysters in the province
as well as their ecological function and the challenges they face. A relatively complete time
series of oyster landings spanning between 1876 and today can be reconstructed from
published information allowing us to retrace the evolution and trends in landings for the last 130
years. This gives a relatively reliable chronological series for the evolution of the oyster
harvesting industry prior to the arrival of aquaculture. Newell (1988) proposed the use of this
kind of time-series as a means to infer information about past standing stocks of oyster reefs.
Based on Newell’s example, data for landings were obtained from a number of sources; from
1876 to 1969 data obtained from Morse (1971); from 1971-1984 data obtained from Jenkins
(1987) in imperial pounds was converted to metric tonnes; from 1984 – 2004 data was compiled
by DFO from statistics obtained via sales slips, shown in the following graph (Figure 7). This
data demonstrates the general trends in the exploitation of natural stock of oysters. It also helps
to illustrate the scale of natural populations prior to current harvests.
At their highest in N.B., reported landings reached a peak in the order of 4,000 t, around
the end of the 1940’s. They had remained between the 1,000 to 1,500 t in the 75 years prior to
that. Since then, NB landings have remained consistently below the 500 t mark, with no
indication of commercial landings returning to pre-Malpeque numbers (Table 10).
Weight (t)
Nova Scotia New Brunswick Prince Edward Island
1st Malpeque
Outbreak PEI
Outbreak NB
Figure 7 - Reported landings of oysters from commercial harvest 1876-2004 (Morse 1971,Jenkins 1987, DFO 2003b).
Table 9 - Estimated historical quantities of oysters in the Maritime Provinces (based on Newell,
1988) compared to present aquaculture and fishery levels.
Gulf NS
Weight (t)
Gulf NB
Weight (t)
Weight (t)
Weight (t)
1870-1900 estimated
oyster biomass
10 161 35 912 130 565 176 638
Estimated total
production (NBDAA,
2006; DFO statistics)
232 1 857 2 849 4 939
Estimated total
production –all sizes
(Comeau, 2006)
1 249
Estimated oyster fishery
landings 65 mm +
(Comeau, 2006)
From these values, and based on Newell’s (1988) approach, we can estimate that there
would have been a standing stock in the order of 176,000 t of oysters in all three Maritime
Provinces prior to the 1900’s; 10,161t for N.S; 35,912 t for N.B. and 130,565 t for P.E.I.
Considering the fact that landings are generally under-reported and that by the turn of the 20th
Century, a number of oyster beds in the Maritimes were already considered depleted (Morse,
1971) it is fair to assume that these numbers would represent a conservative estimate.
Based on the provincial estimates and the Comeau et al. (2006) survey, current
commercial and aquaculture productions combined would represent less than five percent of the
historical biomass of oysters. Therefore, this suggests that the combined standing stock of
oysters found in N.B. estuaries is significantly lower than the biomass that would have been
observed at the turn of the 20th Century. This is consistent with trends reported elsewhere in the
literature (Kirby, 2004).
This historical data of oysters in the Maritime Provinces suggest a high natural carrying
capacity and a natural dominance of oysters in these estuarine ecosystems.
5.2 Characterization of reference state
Reference states are typically established based on pre-activity levels (i.e. before the
introduction of aquaculture). However, as shown above, the “baseline” by which we typically
compare the development of these activities have already shifted drastically from historical
levels. Determining where to locate the benchmark for comparisons and assessing what is a
“natural and productive ecosystem” is difficult given that our current viewpoint is already far
removed from previous levels. The reference state of many estuaries in N.B., as in many areas
on the Atlantic coast of North America, was characterized by an abundance of oysters at a level
which is now difficult to imagine (Gosling, 2003, Kennedy, 1996). The exercise above of
examining historical levels does provide a better perspective for evaluating the scale current
changes in our ecosystems and assessing the role of the oyster as a key component to what
was presumably a diverse, functional and productive ecosystem.
5.3 Ecological benefit characterization
McKindsey et al. (2006) describes effects of shellfish aquaculture on fish habitat. The
report provides detailed information on the role of bivalves in the ecosystem under natural
conditions, describes various shellfish culture methods, and evaluates whether those roles are
mimicked under aquaculture conditions. Their review of literature shows that bivalves are key
components of healthy fish habitat.
Moreover, several of authors have argued that oyster reefs can play a critical role in the
dynamics and resiliency of temperate estuaries. The reader can refer to the extensive review by
Dame (1996): The ecology of marine bivalves, an ecosystem approach. They make the
argument that oysters and their reefs contribute to the robustness of temperate estuaries; for
that reason, they have been termed keystone meta-populations (Dame et al. 1984,Ray et al.
1997); biogenic habitats (Kennedy V.S. 1996,Lenihan 1999,Cranfield et al. 2004,Kirby & Miller
2005); ecosystem engineers (Coen et al. 1999,Gutierrez et al. 2003); essential fish habitat
(DeAlteris et al. 2004); and critical estuarine habitats (Coen et al. 1997,McCormick-Ray 2005).
These ecological roles are summarized in Table 10.
Table 10 - Summary of the functional effects of natural oyster populations on estuarine
components (based on Ray et al. 1997; Kennedy V.S. 1996; Ruesink et al. 2005; McCormick-
Ray 2005)
Adds nutrients and precipitates faeces and pseudofaeces to benthos to feed
demersal feeders, including lobster, crabs and endobenthic organisms. May depress
the ratio of centric diatoms (planktonic and eutrophic waters) in favour of pennate
diatoms (benthic and clear waters).
Biodiversity Provides increased niche space for ecological complexity and faunal abundance;
supports stenohaline species along a salinity gradient; sustains epizoan diversity;
modulate estuarine population structure toward desirable equilibrium. Provide
substrate attachment for plants and invertebrates.
Coupling of
nutrients to
other habitats
Benthic-pelagic coupling of nutrient. Consumption of phytoplankton containing
organic nitrogen NH4+. Enhances N releases by sediment to atmosphere. NH4+ re-
uptake by phytoplankton. Enhances composition of nutrient readily available to SAV.
resilience and
Forms meta-populations and contribute to other communities as sources to restock
disturbed areas; long-term life span of oysters contribute to biomass stability in
estuaries. Increase habitat heterogeneity in the system and increase habitat
redundancy, which can add optional choices in species survival.
Permanent presence of long-lived bivalves exerts effective grazing control on
phytoplankton. High turnover rate potential of estuarine waters. Preferential sorting of
organisms by size, limits impacts on zooplankton; dampens algal blooms; filters
bacteria from water column.
Reefs form discrete hard substrate islands which provide limiting substrate. Shells
provide 3D substrate to other organisms for spawning, nursery and refuge habitats.
1 m2 of shell bottom represents 50 m2 of surface area for epifauna. These organisms
act as food sources for a variety of predators. Reefs provide migration and feeding
halts, creates matrix of seascape habitats which connects resource patches to the
benthos, marshes and other estuarine habitats. Dead shells can help stabilize
benthos, substrate for spat settlement and are recycled over time. Provide refuge
from extreme environmental conditions.
Light regime Removes POM/PIM from water column and enhances depth of Photosynthetically
Active Radiation (PAR).
Feeds on phytoplankton and converts energy into secondary production; release
gametes and larvae which feed other organisms, including zooplankton and other
filter-feeders. Forms spatial nodes of biological activity and couples benthic
heterotrophic activity to intense predator-prey interactions. This helps make
temperate estuaries among the most productive natural systems known (1 514 gCm-
Shoreline and
Reefs buffer against moderate storms and wave actions. Prevent the erosion of
channel banks, stabilize and protect the edges of salt marshes. Mucus-bound
biodeposits have enhanced particle cohesion and can resist erosion. Water flow
patterns. Alters benthic boundary layer and water column hydrodynamics which
enhances particle movements, feeding opportunities and particle dispersions.
5.4 Comparison of alternate states
The critical role of oyster reefs is made the more apparent when they disappear from
estuaries, such has been the case in the eastern United States (Kirby 2004). Rothschild et al.
(1994), for instance, estimated that total oyster habitat in the Maryland portion of Chesapeake
Bay is probably 50% or less of what it was a century ago, that the remaining habitat is of
substantially poorer quality on average, and that the biomass per unit habitat is about 1% of that
at the turn of the century.
Such dramatic reductions in oyster populations are believed to have lead to cascades of
undesirable effects on community and ecosystem dynamics, such as the loss of top-down
control mechanisms on phytoplankton, which may have resulted in increases in nuisance and
toxic algal blooms, reduced water clarity, loss of submerged aquatic vegetation and loss of fish
populations (Kennedy V.S. 1996,Kirby & Miller 2005). It is reasonable to assume that a
comparable state of reduced contribution of the oysters to estuarine ecology exists in our region,
as that historical trend of systematic reef depletion has followed a similar course along the
eastern seaboard (Kirby 2004). This would represent a significant loss to the productivity and
function of these ecosystems as well as a likely reduction in water quality.
The current state is one of depleted natural oyster populations. It is estimated that
populations diminished by more than 90% following the Malpeque disease. In some regions a
100 to 1,000 fold increase in population would be required to restore the desired services
provided by oysters (Luckenbach 2004). Bivalve aquaculture is increasingly recognized as being
critical in providing important ecosystem services and public benefits, such as mitigating water
quality degradation (Powers et al., 2007).
5.5 Significance of ecological benefits
The significance of the ecological benefits of oysters can be observed in the decisions to
invest a great deal of resources in the restoration and reintroduction of oysters. In particular, the
rehabilitation of oyster reefs in temperate estuaries is considered critical in promoting a desirable
state of equilibrium, characterized by a production of fish species considered useful to society
(Ulanowicz & Tuttle 1992, Peterson et al. 2003). They conclude that increasing the number of
oysters, naturally or via aquaculture, would result in increased benthic primary productivity, fish
stocks, and zooplankton densities.
Bivalve shellfish are increasingly considered for their role in restoration programs and their
use in mitigating negative impacts of land use activities (Landry 2002). Over the past years,
DFO-HPSD has issued several Fisheries Act subsection 35(2) Authorizations on projects
located in the estuarine and marine environment. Because these projects (e.g. wharfs, bridges,
etc.) were determined to cause harmful alteration, disruption or destruction (HADD) of fish
habitat, the proponents were required to compensate for lost fish habitat. In the Gulf Region,
most of the marine fish habitat compensation projects are related to reef creation because of
their positive ecological functions (Godin pers. com.). Restoration of oyster reefs is typically
recommended as compensation to offset the damages to fish habitat in other regions of the
world as well, and the net environmental benefits of such interventions are considered positive
(Newell 2004, Kirby & Miller 2005, Newell et al. 2005). Restoration of natural oyster reefs is
recognized as having significant ecological benefit and is often recommended as the preferable
option because of the overall gains in habitat structure and function.
In the United States, the National Oceanic & Atmospheric Administration (NOAA) is
actively involved and making significant investments in the restoration of oyster populations: in
Chesapeake Bay alone, this funding represented 5.4$ million in 2006 (http://chesapeakebay They state that: “At one time, oysters were so abundant in the
Chesapeake Bay that their reefs posed a navigational hazard to ships sailing up the Bay. Now,
because of disease, poor water quality, and decades of overharvest, the oyster population in the
Bay is at about 1% of what it once was. Federal and state agencies, industry, academic
institutions, and nonprofit groups have all been working hard to restore the native oyster
population to levels that will once again provide the level of ecological and economic services
that it once did.
As shown above (e.g. Dealteris 2004; Powers et al. 2007), shellfish aquaculture equipment
can also serve as significant biogenic reefs which can increase the productivity of many
invertebrates and fishes. Although artificial means of increasing oyster populations through
aquaculture may not provide all functions of oyster reefs such as the 3-D habitat associated to
natural reefs (Coen et al. 1999), oysters aquaculture can be considered of significant ecological
benefit (Ulanowicz & Tuttle 1992). Aquaculture of the native oyster can also indirectly provide
broodstock sanctuaries as bottom oyster populations are re-established. There are anecdotal
reports of a number of bays where spawning and settlement of oysters have been restored, with
the presence of water column oyster culture, where none had occurred for a few decades (C.
Noris, personal communication).
5.6 Conclusion on Net Ecological Benefit Analysis
Bivalve culture, by its very nature, is an extractive activity where success is tied directly to
environmental quality, natural supply of larvae and natural food availability. The FAO (2007)
states that the “Culture of molluscs is considered highly environmentally friendly as they do not
require any inputs for growth and utilizes nutrients from the surrounding waters”. In addition to
the value of the oysters themselves, the secondary productivity associated to the culture is also
likely of significant value to fisheries resources (e.g. Powers et al. 2007).
We estimate that the natural population of oysters in N.B. estuaries at the turn of the 20th
Century was approximately twenty times higher than current levels, including wild and
aquaculture levels. Removal of endemic habitat created by oyster reefs has likely resulted in
fragmentation, disturbance or elimination of ecosystem services, and net degradation of
desirable estuarine functions. Newell (1988) suggested that the loss of oysters in Chesapeake
Bay, due to disease and overfishing, contributed to undesirable ecosystem shifts in the food
webs leading to a rise in the biomass of predators such as ctenophores and jellyfish. The author
concluded that “an increase in the oyster population by management and aquaculture could
significantly improve water quality by removing large quantities of particulate carbon”.
There is mounting evidence that increasing the abundance of oysters is likely to restore
some of the ecological services such as water filtration, benthic-pelagic coupling, and top-down
control on phytoplankton once provided by natural stocks. These functions provide net benefits
beyond the provision of fish habitat over an extended time-frame. Oysters in aquaculture
structures are not considered different from oysters in nature. Thus, they can provide a number
of ecological services, which can potentially increase the functional and structural sustainability
of the ecosystem (Prins et al. 1997) and reduce the symptoms of ecosystem distress caused by
eutrophication (Newell 1988, Jackson et al. 2001, Newell & Koch 2004).
Habitat restoration plans increasingly recognize the role of shellfish in improving water
quality by assimilating and recycling large amounts of nutrients by feeding on plankton and thus
aiding to mitigate the effects of anthropogenic eutrophication (Officer et al. 1982). Ferreira et al.
(2007) discusses the economic potential for aquaculture operations as “nutrient sinks” to
essentially remove the nutrient pollution from other industries and profit from this clean-up;
similar to global emission trading mechanisms. In the U.S., in particular, where the loss of the
American oyster has resulted in dramatic shifts in ecosystem equilibrium, there is consensus
that restoration of oyster populations is critical in maintaining ecosystem health.
This Net Ecological Benefit Analysis allowed us to gain a greater perspective on elements
which are not typically considered in an Ecological Risk Assessment. There remains a need to
better understand how distinct habitat types, such as oyster reefs, interact within landscapes in
order to better understand the contribution of aquaculture to supporting complex ecosystem
linkages (Duffy 2006). The exercise of examining both positive and negative effects of shellfish
aquaculture is informative, particularly in illustrating the challenge faced by managers in
weighing the effects of certain activities. This is particularly true when the dynamics of this
activity include non-linear relationships between multiple effects, both positive and negative,
such as the ones associated with increasing shellfish abundance (Figure 8).
We conclude that, when properly managed, oyster aquaculture is likely to provide positive
ecosystem services. This warrants further consideration as a key component in achieving
healthy ecosystem objectives.
Figure 8 – Conceptual figure of relative effects associated to increased abundance of shellfish
(from Newell 2004)
6.1 Identification of appropriate risk management options
The guiding principle for risk management is to achieve a reasonable degree of certainty
that significant adverse effects can be avoided through a rationalised and feasible approach
given the present knowledge limits, available options and resources. The HMP Risk
Management Framework identifies a number of mechanisms to address low risk projects.
Based on the framework and the perceived low risk associated with water column oyster
aquaculture activity through the Ecological Risk Assessment, DFO considered the use of
Operational Statements, letters of advice or Best Management Practices could have been
acceptable options as operational tools to address the level of risk.
However, given the projected growth of the water column aquaculture industry, DFO Gulf
Region favoured that EAs be managed by using the more rigorous Replacement Class
Screening Report (RCSR) approach for this activity. This approach is built on the knowledge of
the environmental effects of a given type of project while consolidating mitigation measures from
governmental federal authorities involved in the process. A RCSR typically includes mitigation
measures and Best Management Practices identical to those normally found in a site-by-site
evaluation and letter of advice. This approach is also favoured because of the heightened public
awareness and scrutiny surrounding aquaculture in general. The approach also implicitly
requires that the authorities reflect on the activity in the context of their longer-term planning and
bay-wide objectives as well as the acceptable levels of development that balance socio-
economic and ecological sustainability.
As explained earlier, a replacement class screening consists of a single comprehensive
report that defines the class of projects and describes the associated environmental effects,
design standards and mitigation measures for projects assessed within the report. It includes a
conclusion of significance of environmental effects for all projects assessed by the replacement
class screening. This type of report presents a summary of the accumulated knowledge on the
environmental effects of a given type of project and identifies measures that are known to
reduce or eliminate the likelihood of these adverse environmental effects. A RCSR is also
considered consistent with the more comprehensive Bay Management Framework (BMF), which
constitutes a broader integrated planning and regulatory framework. In addition, a RCSR is a
living document which includes provisions for revisions every five years, or whenever new
information comes to light. Under a RCSR, yearly reporting of site review to the public registry is
also required.
6.2 Risk Communication
Management of oyster aquaculture will require communication of the findings of this risk
assessment. In N.B., like elsewhere in the world, the emergence of aquaculture as a relatively
new and growing resource use can be perceived to be a disruption of the long-established
status-quo between existing users (Burbridge et al. 2001,Shumway et al. 2003). The recent
growth of aquaculture has occurred along coastlines where there is already a high concentration
of other commercial, recreational and traditional resource users. This can provoke socio-
economic concerns relating to aesthetics, property value and boating access, which is not
unexpected, particularly in prime coastal real estate and recreational areas. In addition, the
utilization of maritime space for aquaculture purposes raises potentially complex property and
federal-provincial jurisdictional issues.
This risk assessment demonstrated that potential risks as they relate to fish and fish
habitat have been identified and that the assessment of likelihood, consequences and probability
of effects is based on reliable scientific evidence. The level of confidence in this approach is
high, particularly in the context of a Bay Management Framework (BMF) where spatio-temporal
interactions with ecological entities are reduced and/or avoided.
6.3 Risk monitoring, reporting and review
Research is being actively conducted by DFO, the Province of N.B., universities and the
aquaculture industry itself. In August 2000, DFO launched its Program for Sustainable
Aquaculture. The program reflects the federal government's commitment to increase scientific
knowledge to support decision-making, strengthen measures to protect human health, and make
the federal legislative and regulatory framework more responsive to public and industry needs.
Specifically, the program allocates $75 million over five years with $15 million each year
thereafter for: 1) environmental and biological science to improve the federal government's
capacity to assess and mitigate aquaculture's potential impacts on aquatic ecosystems; 2) the
Aquaculture Collaborative Research and Development Program, under which DFO partners with
industry by jointly funding R&D projects to enhance sector innovation and productivity; 3)
strengthening of the Canadian Shellfish Sanitation Program; 4) enhancement of the application
of DFO's legislation, regulations and policies that govern aquaculture, particularly as they relate
to habitat management and navigation.
Additionally, monitoring programs are ongoing in order to collect baseline data. For
example, the Shellfish Monitoring Network has standardised cages housing mussels or oysters
in multiple bays in the Maritime Provinces to provide a baseline of shellfish productivity. Also the
Community Aquatic Monitoring Program’s (CAMP) is being conducted in 26 sites in the
Maritimes. CAMP is being used to build working relationships between DFO and community
environmental groups, academia and other interested parties as well as to collect information on
fish and invertebrate communities, water quality (e.g. temperature, pH, nutrients, etc.) and
aquatic vegetation with the collaboration of watershed groups in several bays.
The development of the bivalve aquaculture industry is being closely supervised in N.B.
The New Brunswick Shellfish Aquaculture Environmental Coordination Committee (NBSAECC)
provides a forum for inter-agency communication which tracks the continuously evolving
scientific and technical knowledge related to the activities of this sector and can recommend
changes in shellfish aquaculture management practices when needed. Representatives of DFO,
the Province of N.B., Transport Canada, Environment Canada as well as the New Brunswick
Professional Shellfish Growers Association (NBPSGA) sit on this committee.
Yearly, through the Canada-N.B. MOU for Aquaculture Development, the NBSAECC
meets to review the data resulting from field surveys and research conducted by academics,
federal and provincial agencies. If significant changes occur in the risk posed by the husbandry
methods (e.g. appreciable changes in intensity or techniques), the environmental conditions
(e.g. water quality), or in the state of knowledge concerning water column oyster aquaculture,
they are required to report updated assessments to senior managers of their respective
agencies. The Canada-N.B. Aquaculture Management Committee can thereafter make
decisions to address concerns.
Additionally, the BMF developed with the Province of N.B. is an example of a living tool
and is based on the premises of Adaptive Management to ensure the sustainable development
of the shellfish aquaculture sector. A management team has been established to regularly
review the outcome of the overall planning and regulatory framework to ensure it is regularly
adapted. The team will continue to evaluate the effectiveness of the BMF in regards to
integrated sustainable aquaculture development, based on sound planning and management.
The Habitat Management Program’s Risk Management Framework implicitly recognises
that all activities entail some risks which must be weighed in terms of the scale of negative effect
and the sensitivity of fish and fish habitat using the Risk Assessment Matrix (Figure 3). The
Ecological Risk Assessment characterizes many of the risks and assesses their significance in
the context of the scientific literature and ecosystem dynamics; in summary we conclude that:
The overall scale of potential negative effects of water column oyster aquaculture in
N.B. is low. In general the sensitivity of fish and fish habitat is low, eelgrass which is
being affected by a number of anthropogenic impacts is considered moderately
sensitive. For that reason oyster aquaculture works in N.B correspond to a low-risk
activity on the HMP Risk Assessment Matrix;
Given the low densities observed in water column oyster aquaculture in N.B., which
differ greatly from other regions in the world, for an activity where “most effects of bivalve
aquaculture seem to be related to the scale (intensity and extent) of aquaculture rather
than the type of infrastructure” (DFO 2006), the potential for significant residual effects
after mitigation is low;
Thus the activity is considered unlikely to significantly harm the productive capacity or
the ecological integrity of fish habitat. The risks associated with water column oyster
aquaculture can be managed with adequate planning and mitigation measures through
an adaptive management approach.
The development of this risk assessment has lead to the evaluation of a number of
potential management tools available within DFO’s regulatory mandate. Given the conclusion on
the level of risk, the use of Operational Statements, Best Management Practices, etc is
considered adequate. Because of the heightened public awareness and scrutiny surrounding
aquaculture in general, the use of a RCSR is considered a prudent and appropriate operational
tool for integrating several regulatory and expert advices of federal departments to manage the
level of risk to fish and fish habitat posed by the oyster aquaculture industry.
Although the risk analysis framework generally focuses on negative effects and does not
presently integrate the Net Ecological Benefit Analysis into the decision-making process, we
found the exercise to be informative with regards to evaluating the complexities in ecosystem
dynamics and in qualifying the overall effects of this activity. Accordingly, we believe that
shellfish aquaculture, when managed effectively, can provide many ecosystem benefits and can
contribute to the general environmental health of N.B. estuaries. The Net Ecological Benefit
Analysis also served to illustrate how our current view of temperate estuaries in our region is that
of an altered state (i.e. depleted oyster reefs) in comparison with the reference state which was
dominated by extensive bivalve meta-populations. This conclusion supports the general
approach taken by the HPSD of recommending the development of oyster reefs as
compensation projects for habitat losses. These types of considerations will likely become
increasingly important as governments continue to work towards planning and implementing a
more formal ecosystem approach to managing coastal activities based on regional objectives of
sustainable development.
Firstly, we thank all the participants of the National Science Workshop: Assessing Habitat
Risks Associated With Bivalve Aquaculture in the Marine Environment National Assessment
Process. This workshop and all the related documents that were produced largely inspired this
risk assessment.
We are also grateful to Chad Ziai and Roland Cormier for their assistance and expertise in
the Habitat Management Program and the Risk Assessment Framework.
Special thanks go to Sylvio Doiron, Abel Noël, Dr. Luc Comeau, Claire Carver and Dr.
André Mallet who all contributed to this report with their vast knowledge on oyster aquaculture in
New Brunswick.
We would especially like to thank Dr. Roger Newell and Dr. Christopher Pearce for their
peer-review as well as their constructive comments which were extremely helpful in finalizing
this risk assessment.
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