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ORIGINAL RESEARCH
published: 11 August 2021
doi: 10.3389/fmars.2021.707999
Edited by:
Mhd Ikhwanuddin,
University of Malaysia Terengganu,
Malaysia
Reviewed by:
Valeria Mamouridis,
Independent Researcher, Rome, Italy
Appukuttannair Biju Kumar,
University of Kerala, India
*Correspondence:
Dirk Zeller
dirk.zeller@uwa.edu.au
Specialty section:
This article was submitted to
Marine Fisheries, Aquaculture
and Living Resources,
a section of the journal
Frontiers in Marine Science
Received: 11 May 2021
Accepted: 12 July 2021
Published: 11 August 2021
Citation:
Zeller D, Vianna GMS, Ansell M,
Coulter A, Derrick B, Greer K,
Noël S-L, Palomares MLD, Zhu A and
Pauly D (2021) Fishing Effort
and Associated Catch per Unit Effort
for Small-Scale Fisheries
in the Mozambique Channel Region:
1950–2016.
Front. Mar. Sci. 8:707999.
doi: 10.3389/fmars.2021.707999
Fishing Effort and Associated Catch
per Unit Effort for Small-Scale
Fisheries in the Mozambique
Channel Region: 1950–2016
Dirk Zeller1*, Gabriel M. S. Vianna1, Matthew Ansell1, Angie Coulter2, Brittany Derrick2,
Krista Greer2, Simon-Luc Noël2, Maria L. Deng Palomares2, Audrey Zhu2and
Daniel Pauly2
1Sea Around Us – Indian Ocean, School of Biological Sciences and Oceans Institute, University of Western Australia,
Crawley, WA, Australia, 2Sea Around Us, Institute for the Oceans and Fisheries, University of British Columbia, Vancouver,
BC, Canada
The Mozambique Channel region in East Africa has diverse marine ecosystems and
serves as a migratory corridor for economically important species. Local and foreign
industrial fisheries operate in the Mozambique Channel, but regional small-scale fisheries
are the crucially important fisheries that provide food security, livelihoods, and economic
opportunities for rural coastal communities. This study reconstructed and investigated
trends in the fishing effort and catch per unit effort (CPUE) of small-scale marine fisheries
in four Exclusive Economic Zones (EEZ) that constitute the Mozambique Channel,
i.e., Union of Comoros, Madagascar, Mayotte, and Mozambique, from 1950 to 2016.
Effective fishing effort for small-scale fisheries in the form of fishing capacity in kWdays
(i.e., kilowatt days) was derived using the number, length, motorization (engine power)
by fishing vessels, as well as an approximate human-powered equivalent for shore-
based fishers without vessels, as well as days of fishing per year. Effective small-scale
fishing effort in the Mozambique Channel increased by nearly 60 times from just over
386,000 kWdays in 1950 to over 23 million kWdays in 2016. Correspondingly, the
overall small-scale CPUE, based on previously and independently reconstructed catch
data declined by 91% in the region as a whole, from just under 175 kg·kWday−1in
the early 1950s to just over 15 kg·kWday−1in recent years. All four EEZs showed the
strongest declines in the small-scale CPUE in the earlier decades, driven by motorization
and growth in vessel numbers impacting effective fishing effort. Increased motorization
combined with a substantial growth in overall vessel numbers were the drivers of the
increasing fishing effort and decreasing CPUE, and clearly suggest that continuing to
increase the fishing capacity of small-scale fisheries in the absence of effective and
restrictive management actions may exacerbate overexploitation risk.
Keywords: artisanal fisheries, CPUE, fishing capacity, Madagascar, Mayotte, Mozambique, subsistence fisheries,
Union of Comoros
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Zeller et al. Mozambique Channel CPUE and Effort
INTRODUCTION
The Mozambique Channel region in East Africa separates
Madagascar from the African continent (Figure 1) and is
characterized by high marine biodiversity and a variety
of ecosystems, including a large proportion of the Indian
Ocean’s coral reefs, mangroves, and seagrass beds (Nunes
and Ghermandi, 2015). It is also an important corridor
for migratory species, such as tuna (Nunes and Ghermandi,
2015). The four countries/territories directly associated with the
Mozambique Channel region, namely the Union of Comoros,
Madagascar, Mayotte, and Mozambique all heavily depend on
small-scale domestic fishing (artisanal and subsistence fishing).
For example, the Comoros lacks domestic industrial fisheries and
an aquaculture sector (FAO, 2015a); however, between 2005 and
2009, domestic marine fish resources accounted for 60–70% of
the animal protein consumed by Comoros islanders (Béné and
Heck, 2005;Kurien and López Ríos, 2013;Breuil and Grima,
2014a). For Madagascar, the Food and Agriculture Organization
of the United Nations (FAO) reports that the small-scale fishing
fleet was responsible for over half of total domestic marine fish
catches in 2008 (FAO, 2009). Despite their importance to food
security and local livelihoods, small-scale fisheries catches in the
region have been widely underreported (Jacquet et al., 2010;Le
Manach et al., 2012b;Genay and Merceron, 2017;Anon, 2019c).
For example, the reconstructed catch data of the Sea Around Us,1
which complement officially reported data with comprehensive
estimates of unreported catches (Zeller et al., 2016), suggest that
small-scale catches in Madagascar actually may account for over
80% of the total domestic marine fish catch (Le Manach et al.,
2012b), as opposed to the 53% suggested by FAO (2009) based on
officially reported data. The underrepresentation of small-scale
fisheries is a common issue globally, which contributes to the
marginalization in socio-economic and political considerations
(Pauly, 2006;Schuhbauer and Sumaila, 2016;Teh et al., 2020)
as well as in official statistics (Pauly and Charles, 2015;Zeller
et al., 2015;Pauly and Zeller, 2016a), despite more recent efforts
to begin addressing this issue (FAO, 2015b).
Since 1950, the coastal populations of the four inhabited
countries/territories associated with the Mozambique Channel
have increased, and marine catches have correspondingly also
grown (Jacquet et al., 2010;Le Manach et al., 2012b;Doherty
et al., 2015a,b;Genay and Merceron, 2017). The exceptions
are the uninhabited islands of Juan de Nova, Europa, and
Bassas da India that are territorial possessions of France, here
referred to as the “Mozambique Channel Isl. (France)” (Figure 1).
These waters are not fished by “domestic” fleets due to the
uninhabited nature of the islands, but are accessed by fishers
from surrounding areas as well as by distant water fleets
(Le Manach and Pauly, 2015). Given the crucial importance
of locally sourced seafood for domestic food security and
nutrient security for the Mozambique Channel region, demand
will likely continue to increase. However, official fisheries
statistics describing the small-scale fisheries catches in this region
remain limited.
1www.seaaroundus.org
Historically, FAO presumed that small-scale artisanal and
subsistence fishers were likely only temporary features during an
anticipated transition to industrial fisheries (Panayotou, 1982).
Therefore, institutional and political support had been, and
often still is, skewed toward large-scale (i.e., industrial) fisheries
due to perceived higher direct macroeconomic contributions to
national or government income (Zeller and Pauly, 2019). As such,
industrial fisheries often have easier access to subsidies, including
subsidized development loans (Panayotou, 1982;Harper et al.,
2012;Bellmann et al., 2016;Sumaila et al., 2019). More recently,
the international community began to recognize the crucial
nutrient security and food security, livelihood, and socio-
economic importance of small-scale fisheries (FAO, 2015b;
Golden et al., 2016;Teh et al., 2020;Vianna et al., 2020),
although officially reported statistics as published by the FAO
on behalf of countries continue to be hampered by an absence
of fishing sector differentiation (Pauly and Charles, 2015). In
contrast, such sectoral differentiation is an integral and core
feature in the Sea Around Us reconstructed catch data for all
countries (Pauly and Zeller, 2016a,b), which allows for a more
accurate and comprehensive examination of the importance of
small-scale sectors at the country, regional and global level
(Zeller and Pauly, 2019), including their economic importance
(Zeller et al., 2006).
Here, a data reconstruction approach based on Zeller
et al. (2016) was used to derive time series estimates of
small-scale fishing effort from 1950 to 2016 for each of
the four inhabited Mozambique Channel countries/territories.
These effort estimates were then combined with independently
reconstructed small-scale catch data from the Sea Around Us for
each of these countries/territories (Pauly and Zeller, 2016a,b) to
derive small-scale catch per unit effort (CPUE) estimates for the
same time period.
MATERIALS AND METHODS
In this study, small-scale fishing effort for each country/territory
was reconstructed using the same general data reconstruction
approaches and principles as used earlier and independently
by the Sea Around Us for catch data reconstruction (Zeller
et al., 2016). Data reconstructions essentially aim to complement
officially reported data with best estimates of unreported
components, using a wide variety of secondary data and
information sources combined with carefully vetted and clearly
stated, conservative assumptions (Zeller et al., 2016). To ensure
independence of the two key datasets being used here (small-
scale catches and fishing effort), fishing effort was reconstructed
without considering previously reconstructed small-scale catch
data in each country (Pauly and Zeller, 2016a,b).
Study Area
The Mozambique Channel region (IHO, 1953) lies between
the East African coast and the west coast of Madagascar
(Figure 1). The northern boundary of the channel is marked by
the estuary of the River Rovuma in Mozambique (10.46◦
S and 40.43◦E) and the north west point of Grande
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Zeller et al. Mozambique Channel CPUE and Effort
FIGURE 1 | The Mozambique Channel region and the EEZs of the countries or territories considered here: Union of the Comoros, Madagascar, Mayotte, and
Mozambique. The uninhabited Mozambique Channel Islands administered by France are indicated as well, but have no domestic, resident small-scale fisheries and
thus no resident small-scale effort or catches.
Comore/Ngazidja (the northernmost island of the Comoros
Isl. Group; 11.95◦S and 49.28◦E). The southern boundary
of the channel runs from the southern tip of Madagascar
to Ponta do Ouro, Mozambique (26.88◦S and 32.93◦E).
Within the channel, there are five Exclusive Economic
Zones (EEZs): Union of Comoros Islands, Madagascar,
Mayotte, Mozambique, and the minor Mozambique Channel
Islands, comprising the uninhabited French dependencies
of Juan de Nova, Bassas da India, and Europa Islands
(Figure 1).
The focus of this study was on small-scale domestic fisheries
by resident fishers, and included the EEZs of the Union of
Comoros, Madagascar, Mayotte, and Mozambique. The French
dependencies here referred to as the Mozambique Channel
Islands are uninhabited, and therefore by the definition of
small-scale sectors used here (Zeller et al., 2016) have no
locally based domestic small-scale fleets, and thus did not
contribute to this study. However, their waters are being fished
by neighboring countries, including by artisanal and recreational
vessels, as well as French and distant-water industrial fleets
(Le Manach and Pauly, 2015).
Boat-Based Fishing Effort
Nominal fishing effort (kW), as defined in this study, is the
product of total small-scale fleet capacity. A fleet is the number
of vessels with a similar capacity, i.e., in the same length class and
motorization category, and utilizing the same or similar fishing
gears. Engine capacity per fishing vessel (kW) in a given fleet
was determined by length and motorization (Table 1). Thus,
total nominal fishing effort is the product of the engine capacity
and the number of boats operating within a fleet segment in
a given year. Non-motorized vessels were considered to have
equivalent capacity of 0.37 kW·vessel−1for vessels of length class
1 and 0.75 kW·vessel−1for vessels of length class 2 (Table 1),
based on Greer et al. (2019a).
Effective fishing effort (kWdays) is the product of nominal
fishing effort (engine capacity ×number of boats within a fleet
segment) in kW and the number of days spent fishing per year.
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Zeller et al. Mozambique Channel CPUE and Effort
The number of days spent fishing per year (i.e., fishing trip days)
for each fleet segment was a major aspect of the research in
this project (see country details in Supplementary Material).
Unfortunately, there was a notable knowledge and data gap
in this metric in the literature, thus requiring conservative
assumptions to be able to derive likely time series for fishing
days. If no specific data were found for a given fleet segment,
conservative assumptions, and approximations were used to
derive an average number of fishing trip days per year. Due
to the generally low technological development of most small-
scale vessels in the Mozambique Channel region, we did
not apply a “technology creep” factor to our effort estimates
(Palomares and Pauly, 2019).
Shore-Based Fishing Effort
Fishing and seafood collecting from shore without the use of a
boat, often largely conducted by women, is a regular activity in
many parts of the study region and globally (Harper et al., 2013,
2020;Zeller et al., 2015). Given its widespread existence, this
fishing component needs to be accounted for in the estimation
of overall small-scale fishing effort.
The nominal fishing effort or fishing capacity of one shore-
based fisher is assumed to be approximately 0.08 kW of engine
equivalence per work (fishing) day (Krendel et al., 2007). Thus,
shore-based fishing activities were converted to the equivalent
nominal fishing effort (kW) by multiplying the number of
shore-based fishers by their assumed engine equivalency of
0.08 kW (Table 1).
Effective fishing effort (kWdays) was calculated by multiplying
the nominal fishing effort for shore-based fishers with the average
number of days per year for which fishing from shore occurred.
Fishing days for shore-based fishers were determined from
country-specific sources wherever available (see country details
in Supplementary Material). If no specific data were found for
a given country, conservative assumptions, and approximations
were used to derive an average number of fishing trip days per
year. We recognize that shore-based fishers do not necessarily
fish all day, i.e., for a full “work day,” with regards to the
engine equivalency used above. However, as we remained
conservative in our estimation of the number of shore-based
fishers throughout, we consider our assumption of a full work
day engine power equivalency for shore-based fishers to be an
acceptable approximation.
TABLE 1 | Assumed and derived engine capacity of motorized and non-motorized
fishing vessels by length class for small-scale vessels based on Greer et al.
(2019a), as well as engine capacity-equivalency for shore-based fishers.
Length class Length (m) Mean length(m) Capacity (kW)
Motorized Non-motorized
1<7.9 4.5 9.11 0.37
2 8–15.9 11.3 58.70 0.75
Shore-based NA NA NA 0.08
Length classes over 15.9 m were considered to be industrial vessels and
thus not used here.
Country Details
Union of Comoros
Prior to gaining independence in 1975 as the Union of Comoros,
the Comoros Archipelago was a French colony. The Comoros
Archipelago includes the island of Mayotte, which remains a
French colony and is thus examined separately (see Figure 1 and
below). The population of the Union of Comoros is concentrated
on three islands: Ngazidja in the northwest, Mwali, located
centrally, and Nzwani in the east (Figure 1). Comoros declared
its 165,000 km2EEZ in 1976, and has an Inshore Fishing Area
of around 1,500 km2.2Inshore Fishing Areas are defined as the
area that extends from shore to either 50 km offshore or to the
200 m depth contour, whichever comes first (Chuenpagdee et al.,
2006). Inshore Fishing Areas are thought to represent the majority
coastal sea-space along inhabited coastlines within which small-
scale fisheries would likely operate (Chuenpagdee et al., 2006;
Chuenpagdee, 2011).
Approximately 18% of the population of Comoros was
estimated to live below the international poverty line in 2014
(Anon, 2019a). Marine fisheries are crucially important for food
security, and exports and imports of fish products are limited,
thus most fish are consumed directly in the country (FAO,
2015a). Comoros does not have a truly domestic industrial
fleet, or distinct recreational fishing. Fishing is characterized by
small-scale artisanal and subsistence activities of local fishers,
predominantly using hand lines, gillnets and surface nets.
The detailed estimation methods for the small-scale fishing
effort are presented in Supplementary Material. There were
several data sources stretching back to the mid-1950s for the
number of small-scale fishing vessels in the Comoros, with
motorization starting in the late 1970s (Supplementary Table 1).
Several types of vessels are used in the Comoros: the more
traditional motorized or non-motorized pirogues of up to 7 m
length, or the more modern motorized vedettes of between 6
and 12 m in length. Data on shore-based fishers was limited,
and required assumptions to estimate shore-based fishing activity
(Supplementary Table 2). Women actively fish and collect
seafood (i.e., gleaning) from shore in the Comoros (Hauzer et al.,
2013), which we estimated as part of total shore-based effort
(Supplementary Table 2).
Madagascar
Madagascar represents the eastern boundary of the Mozambique
Channel (Figure 1), with an EEZ of over 1.2 million km2and
an Inshore Fishing Area (Chuenpagdee et al., 2006) of over
113,000 km2.3
Until its independence in the 1960s, Madagascar was a
French colony. Madagascar’s political history since then has been
marked with multiple regime changes, and the country remained
politically unstable (Ploch and Cook, 2012). There is a high
rate of poverty, with an estimated 75% of the population living
under the international poverty line in 2018 (Anon, 2019b).
Although the east is more densely populated, most of the fishing
is conducted off the west coast (Le Manach et al., 2012b). In
2www.seaaroundus.org/data/#/eez/174
3www.seaaroundus.org/data/#/eez/450
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Madagascar, marine fishing is an important source of food and
exports, particularly in coastal areas where agriculture cannot or
is not practised (Le Manach et al., 2012b).
The small-scale fishing sector consists of fishers on foot
as well as “traditional” boat-based fishing in wooden dugout
canoes (these can be motorized), with both these components
engaging in artisanal as well as subsistence fishing. Locally, the
artisanal sector is considered to include motorized boats with
engine power up to 50–60 HP, including shrimp trawlers and
“catchers,” dories and collection vessels for fisheries products
such as sea cucumbers (Andrianaivojaona et al., 1992;ASCLME,
2011). Although the FAO/Indian Ocean Commission’s Smartfish
program consider smaller shrimp trawlers to be artisanal
(Andrianaivojaona et al., 1992;Mngulwi, 2006;Breuil and Grima,
2014b), the Sea Around Us follows the definition of Martín (2012)
and classifies all trawler catch as being industrial regardless of
vessel size (Zeller et al., 2016). Therefore, shrimp trawlers were
not included in the calculation of small-scale fishing effort and
CPUE in this study.
The detailed estimation methods for the small-scale
fishing effort are presented in Supplementary Material.
There were several data sources for the number of fishing
vessels in Madagascar, stretching back to the mid-1960s, with
motorization starting in 1970 (Supplementary Tables S3, 4).
A substantial number of people in Madagascar fish without boats
(Andrianaivojaona et al., 1992;Breuil and Grima, 2014b), and
the number of shore-based fishers over time was assumed to
correlate to the total Madagascan population (Supplementary
Table 3). There was very little information on the number of
days fished per year by small-scale vessels in Madagascar, with
reports from the 1980s suggesting between 150 and 220 days per
year (Rey, 1982), while shore-based fishers were thought to fish
around 20 days per month in 2009 (Barnes and Rawlinson, 2009)
or 240 days per year (Supplementary Table 5).
Mayotte
Mayotte, a French territory, is an island located east of the
Union of Comoros within the Comoros Archipelago (Figure 1).
The EEZ of Mayotte, declared in 1978, has an area of nearly
63,000 km2and an Inshore Fishing Area (Chuenpagdee et al.,
2006) of roughly 1,600 km2.4Mayotte is the poorest of France’s
overseas territories; however, the Gross Domestic Product of
the island is higher than that of the other countries in the
Mozambique Channel, and it is generally considered to be more
developed than its neighbors. As a result, Mayotte is a major
destination for illegal immigration (Genay and Merceron, 2017).
The large and growing population and resultant food security
strain on the marine environment pushed Mayotte in 2010
to declare its entire EEZ as a marine protected area (Anon,
2012). Mayotte’s population is dependent on marine fisheries
as a primary source of protein, and many of its villages are
concentrated along the coast (Guézel et al., 2009).
The detailed estimation methods for the small-scale fishing
effort are presented in Supplementary Material. As a French
territory, data for Mayotte are incorporated in national French
4www.seaaroundus.org/data/#/eez/175
statistics; however, these data are not easily disaggregated
between Mayotte and other French territories in the Indian
Ocean. Reported numbers of small-scale fishing boats exist in
five categories: small, medium, and large pirogues, and barques, as
well as small longliners in recent years. These data were available
for multiple years between 1962 and 2015 from various sources
(Supplementary Table 6). Motorization started in the 1970s
through the introduction of outboard motors for large pirogues
(Jacquemart, 1980), with a small proportion of small and medium
pirogues being motorized in subsequent years (Supplementary
Table 7). There was minimal quantitative information on shore-
based fishing in Mayotte, and the number of shore-based fishers
was assumed proportionate to the total Mayotte population over
time. Accurate estimates of the number of fishing days were not
available for all small-scale fleet components in Mayotte, and
approximations were required based on similar fleet components
in Mayotte or the Mozambique Channel region.
Mozambique
Mozambique is located on the southeast coast of mainland Africa
and makes up the western border of the Mozambique Channel.
The EEZ of Mozambique, declared in 1976, has an area of
over 571,000 km2and the Inshore Fishing Area (Chuenpagdee
et al., 2006) is over 68,000 km2.5Formerly a Portuguese colony,
the country gained its independence following a decade-long
war from 1964 to 1974. Shortly thereafter, a civil war erupted
from 1977 to 1992. Since the first democratic elections in
1994, Mozambique has been relatively stable politically, with
economic reform and the resettlement of civil war refugees
leading to a high growth rate in both the population and
the economy (Bueno et al., 2015). However, the country
suffers from wealth inequality (Anon, 2018). Since the mid-
2010s the country has faced a growing insurgency by Islamist
groups, mainly in the northern region of Cabo Delgado,
which has increased the political and socio-economic instability.
Small-scale fisheries continue to contribute substantially to
food security and livelihoods in coastal communities, while
government support is often directed to industrial, cash-revenue
generating fisheries (Jacquet and Zeller, 2007;Jacquet et al.,
2010). Wooden canoes make up most of the small-scale fleet,
and the most widespread gears used are gillnets and beach seines
(Oceanic Développement and Mega Pesca Lda, 2014).
The detailed estimation methods for the small-scale fishing
effort are presented in Supplementary Material. There were data
for the number of fishing vessels in Mozambique for multiple
years back to the early 1950s (Supplementary Table 8), and
unlike the other countries/territories in this study, motorization
started before 1950 (FAO, 1958). The total number of shore-based
fishers were reported for multiple years since 1995, but required
adjustments to exclude freshwater statistics from the combined
data in 2007 and 2012. Prior to 1995, the number of shore-based
fishers was assumed to correlate with the total population back
to 1950 (Supplementary Table 9). This proportion was adjusted
across several time periods to account for increased migration
to coastal regions due to the internal conflicts. As described in
5www.seaaroundus.org/data/#/eez/508
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Supplementary Table 10, the average number of days per year
spent fishing was approximated based on Hara et al. (2001) and
insights from Jacquet and Zeller (2007).
Catch per Unit Effort
Catch per unit of effort is a basic fisheries science measure often
used as a first-order evaluation of broad trends in likely relative
abundance or relative biomass trends over time of the underlying
fish stocks (Skalski et al., 2005;Belhabib et al., 2018). While
CPUE has its limitations, it can be useful in long-term trend
monitoring of a fishery, particularly where more detailed data and
stock assessments do not exist (Stamatopoulos, 2002) and open
or semi-open access fisheries predominate, i.e., where restrictive
fisheries management actions may be absent or ineffective.
Here, the small-scale fisheries catches for each country/territory
in the Mozambique Channel region were extracted from the
Sea Around Us global reconstructed catch database (see text
footnote 1) for 1950–2016 (Pauly and Zeller, 2016a,b). These
catch data were previously and independently reconstructed
for the Union of Comoros (Doherty et al., 2015a), Mayotte
(Doherty et al., 2015b), Mozambique (Jacquet and Zeller, 2007;
Jacquet et al., 2010), and Madagascar (Le Manach et al., 2011,
2012a,b), and conservatively updated to 2016 (Derrick et al.,
2020). CPUE is the quotient of the annual small-scale total catch
per country as derived independently through Sea Around Us
catch reconstructions and the annual effective small-scale fishing
effort as reconstructed here.
RESULTS
Fishing Effort
Effective small-scale fishing effort in the entire Mozambique
Channel region grew slowly but steadily from around
386,000 kWdays in 1950 to around 2.6 million kWdays
in the mid-1970s, increasing more steeply thereafter and
reaching approximately 23 million kWdays by 2016 (Figure 2A
and Table 2). Thus, overall small-scale fishing effort in the
Mozambique Channel region increased nearly 60-fold since
1950. This increase was dominated by growth in fishing effort
in Madagascar since the mid-1980s and in Mozambique
since the 1990s, although the other countries/territories also
grew in effective effort over the 67-year period considered
here (Figure 2A).
For the region as a whole, shore-based effective fishing effort
was almost equal to boat-based effective fishing effort in the first
few years, with boat-based effort growing 96-fold from around
220,000 kWdays in 1950 to approximately 21 million kWdays
by 2016 (Figure 2B and Table 2). This substantial growth in
boat-based fishing effort was driven by massive increases in the
number of boats, as well as the motorization trend in many of
the countries after 1970, especially the Comoros and Mayotte
(Figures 2C–E and Table 2). Only Mozambique maintained a
substantial shore-based effort trend over time, although boat-
based effort increased strongly after the late 1990s (Figure 2F).
Importantly, however, both Mozambique and Madagascar seem
to be experiencing an increase in shore-based fishing effort in the
most recent years (Figures 2D,F).
Catch per Unit Effort
The previously and independently reconstructed small-
scale marine catches for the Mozambique Channel
countries/territories displayed an overall fivefold increase
over the 1950–2016 time period, growing from approximately
67,000 tonnes in 1950 to over 350,000 tonnes in 2016 (Figure 3A).
Small-scale catches in the Mozambique Channel region were
dominated by Mozambique and Madagascar (Figure 3A), which
was to be expected, given their substantially larger populations,
long coastlines and large coastal fishing areas. Small-scale
catches in the Comoros Islands increased slowly from around
1,000 tonnes in 1950 to just over 4,000 tonnes in 1978, before
increasingly strongly through the 1980s and early 1990s. Growth
in catches slowed through the 1990s, and catches plateaued
around 18,500 tonnes year−1in the mid-2010s (Figure 3B). The
catches of small-scale fisheries in Madagascar grew near linearly
from around 14,000 tonnes in 1950 to 136,000 tonnes in 2016
(Figure 3C). Catches in Mayotte increased from 237 tonnes in
1950 to just over 2,600 tonnes in 1995 (Figure 3D). Thereafter,
catches entered a period of strong fluctuations throughout the
late 1990s and early 2000s, before increasing again strongly to
over 3,100 tonnes by 2016 (Figure 3D). Mozambique’s small-
scale catches were strongly influenced by the civil war driven
coastal migrations during the 1960–1990 period (Blythe et al.,
2013), with catches first increasing from around 51,500 tonnes
in 1950 to an initial peak of just under 147,500 tonnes in 1979
(Figure 3E). Thereafter, catches declined to approximately
79,700 tonnes in 2005, before increasing again during the 2000s
and especially since 2013 to a new all-time peak of just over
192,500 tonnes in 2016 (Figure 3E).
Overall, the small-scale CPUE estimates for the entire
Mozambique Channel region, as derived from the combination of
the previously reconstructed catches and presently reconstructed
fishing effort data suggested a decline of 91% between 1950
and 2016, from around 174 kg·kWday−1in 1950 to just over
15 kg·kWday−1by 2016 (Figure 4A). The strongest decline
in CPUE was observed during the 1950s, after which the rate
of decline slowed until the mid-1980s; thereafter, the CPUE
continued to decline at a slower rate (Figure 4A).
The small-scale fisheries CPUE in the Comoros Islands
initially experienced an increase, from 19.3 kg·kWday−1in 1950
to the time series maximum of 27 kg·kWday−1in 1962, after
which the CPUE declined strongly to a low of 6.3 kg·kWday−1
in 1989 (Figure 4B). The CPUE recovered slightly in the early
1990s before starting a steady decline to the all-time low of
4.3 kg·kWday−1by 2016. Overall, the small-scale CPUE in
the Comoros Islands declined by approximately 78% between
1950 and 2016 (Figure 4B). The CPUE for the small-scale
fisheries on Madagascar stayed relatively constant at a high
level of around 110 kg·kWday−1during the 1950s and 1960s,
reaching a time series maximum of 117 kg·kWday−1in 1969
(Figure 4C). Starting in 1970, the CPUE began a strong decline
to around 32 kg·kWday−1in the late 1980s, after which the
decline tapered off somewhat, before leveling out at around
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Zeller et al. Mozambique Channel CPUE and Effort
FIGURE 2 | Annual effective fishing effort (kWday ×106) between 1950 and 2016 for small-scale fisheries in (A) the Mozambique Channel region by country; (B) the
Mozambique Channel region by boat- versus shore-based fisheries; (C) Comoros; (D) Madagascar; (E) Mayotte; and (F) Mozambique. Start year of motorization is
indicated.
TABLE 2 | Effective fishing effort (kWdays) of the four Mozambique Channel entities and the entire Mozambique Channel region examined for 1950 and 2016.
Area Shore-based effective fishing Boat-based effective fishing Total effective fishing
effort (kWdays ×106) effort (kWdays ×106) effort (kWdays ×106)
1950 2016 1950 2016 1950 2016
Comoros 0.010 (6%) 0.06 (3%) 0.05 (22%) 4.40 (21%) 0.06 (15%) 4.46 (19%)
Madagascar 0.045 (27%) 0.56 (25%) 0.08 (39%) 5.79 (28%) 0.13 (34%) 6.35 (27%)
Mayotte 0.001 (1%) 0.03 (1%) 0.01 (3%) 1.94 (9%) 0.01 (2%) 1.97 (8%)
Mozambique 0.111 (66%) 1.57 (71%) 0.08 (36%) 8.93 (42%) 0.19 (49%) 10.51 (45%)
Region 0.17 2.22 0.22 21.07 0.39 23.29
Percentage values indicate the contribution to the total regional effective fishing effort of each component in each year.
22 kg·kWday−1by 2016 (Figure 4C). The overall decline of
small-scale CPUE on Madagascar was 80% over the 60+year
time period considered here. The CPUE of Mayotte’s small-scale
fisheries declined starting in 1950 from 30 kg·kWday−1through
the 1950s before tapering off in the late 1960s at around
21 kg·kWdays−1(Figure 4D). The introduction of motorization
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Zeller et al. Mozambique Channel CPUE and Effort
FIGURE 3 | Previously and independently reconstructed catches (tonnes ×103) for small-scale fisheries from 1950 to 2016 for (A) the Mozambique Channel region
by country; (B) Comoros; (C) Madagascar; (D) Mayotte; and (E) Mozambique.
in Mayotte’s fleets after 1970 led to a very rapid and massive
decline in the derived CPUE in the early-1970s, before reaching
a very low level of around 1.5 kg·kWday−1in the early 1980s
(Figure 4D). The CPUE fluctuated slightly around this level
ever since, resulting in an overall CPUE decline of 95% since
1950 (Figure 4D). The CPUE of the small-scale fisheries in
Mozambique declined strongly and rapidly from very high levels
of 272 kg·kWday−1in 1950 to just over 100 kg·kWday−1by the
early 1960s (Figure 4E). It continued to decline more gradually
over the remainder of the time period to reach very low levels
of around 13 kg·kWday−1by the early-2010s, before increasing
again very modestly to 18 kg·kWday−1by 2016 (Figure 4E).
Overall, this resulted in a decline in CPUE of 93% since 1950
(Figure 4E).
DISCUSSION
A considerable variety of different and non-standardized
measures of fishing effort are used around the world, which
makes global comparisons difficult. Fortunately, a standardized
measure of effort using the power input in fisheries, i.e., kWday,
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Zeller et al. Mozambique Channel CPUE and Effort
FIGURE 4 | The catch per unit effort (CPUE) for small-scale fisheries (kg·kWday-1) from 1950 to 2016 for (A) the complete Mozambique Channel region;
(B) Comoros; (C) Madagascar; (D) Mayotte; and (E) Mozambique. Start year of motorization is indicated.
is now available globally (Parker et al., 2018;Greer et al., 2019a,b),
enabling international comparisons. This finally permits direct
comparisons between fisheries, gear-types, regions countries, and
globally to be undertaken in a standardized fashion. Here, we
used a data reconstruction approach (Zeller et al., 2016) to refine
and update the preliminary fishing effort data of Greer et al.
(2019a) for small-scale fisheries from 1950 to 2016 in the four
inhabited countries or territories that make up the Mozambique
Channel region off East Africa (Figure 1). Furthermore, we
combined the small-scale fishing effort time series data derived
here with previously and independently estimated small-scale
catch data for these countries/territories (Jacquet and Zeller,
2007;Jacquet et al., 2010;Le Manach et al., 2011, 2012b;Doherty
et al., 2015a,b,c), obtained using the catch data reconstruction
approach of Zeller et al. (2016), to develop CPUE time series
for the small-scale fisheries in the Mozambique Channel region
from 1950 to 2016.
Overall, our results illustrated consistent and strong increases
in fishing effort over the 67-year period considered here. This
growth in effort was driven not only by increasing motorization,
but also by considerable increases in the number of small-scale
fishing boats being used. Crucially, the combined catch and
fishing effort data clearly demonstrated consistent and strong
declines in the CPUE of small-scale fisheries in every country
or territory examined, with CPUE declining by 91% across
the region. The geographically smaller entities of Comoros and
Mayotte had CPUE declines of 78 and 95%, respectively, while
CPUE declines of 80 and 93% were observed for Madagascar and
Mozambique, respectively. Declining CPUE time series trends,
especially in the absence of effective effort-controlling fisheries
management, generally suggest declining relative abundances
of the underlying fished stocks (Hoggarth, 2006). Thus, the
pattern of CPUE observed here suggests a strongly declining
fisheries resource base for the small-scale fisheries in these
countries/territories over the last 60+years, impacting a crucial
food security sector in this region of Africa. This trend is in
general agreement with a recent assessment of the biomass
patterns of exploited stocks for the tropical Indian Ocean region,
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Zeller et al. Mozambique Channel CPUE and Effort
which suggested general declines in stock biomass of around 60–
70% from levels in 1950 (Palomares et al., 2020). Furthermore, the
overall levels of catches, including industrial and foreign fishing,
in the Agulhas Current Large Marine Ecosystem, which includes
the Mozambique Channel entities considered here, have been
declining steadily since peaking in the late 1960s (Figure 3 in
Zeller et al., 2020).
Effective fishing effort was calculated here using four core
fishing capacity parameters: (1) the number of boats, (2) the
length of boats, (3) the engine power (kW) of boats, with non-
motorized boats being assigned an approximate human-power
equivalent, and (4) the number of days boats fish in a year
(fishing days). Shore-based small-scale fishing without boats was
also included in the fishing effort estimation, using the number
of shore-based fishers, shore-based fishing days and a human-
power equivalent. This ensured comprehensive coverage of all
small-scale fishing in each country and territory. Estimating
broad-scale fishing effort based on indirect methods such as
used here relies on assumptions that, no matter how carefully
and conservatively made, are inherently uncertain, which has
generated some debate in regards to the potential accuracy of
the data (Greer et al., 2019b;Ziegler et al., 2019). However, our
extensive use of a range of available fishing capacity parameters
sourced at the fisheries- and country-level may provide some
advantages over more generalized estimation techniques, and is
thought to provide a reasonable representation of the fishing
effort trends in the region over time.
The increase in small-scale fishing effort we documented
here was the combined result of growth in both the number
of boats as well as motorization of fleets. The introduction and
popularization of motorization of traditional vessels, and the
introduction of newer, larger powered vessels were important
factors driving fishing effort trends. Mayotte, for example, had
the lowest effective fishing effort in 1950, with no motorized
fishing vessels. With the introduction of motorization after 1970,
effective fishing effort steeply increased over the subsequent
decade as fleets rapidly motorized. In contrast, the small-scale
fishing fleets in Madagascar were the largest in terms of number
of boats, and although its effective fishing effort is still increasing
due to continuing growth in the number of non-motorized
vessels, the very low proportion of vessels that are motorized
(0.03% in 2016) limits the fishing power and fishing capacity of
its large small-scale fleet.
Clearly, the four parameters used here to estimate effective
fishing effort do not necessarily capture all aspects of vessel
and fishing capacity. Most fishing effort models, including the
one we used here, do not implicitly account for the impacts
of technological advances on effort measures over time (i.e.,
technology creep), such as the introduction and spread of
synthetic material in fishing gear, sonar, GPS, refrigeration or
fish aggregating devices (Palomares and Pauly, 2019). Technology
creep is pronounced in industrial fishing fleets over time, and is
likely to have increased the fishing capacity of industrial vessels
in the region, further contributing to overfishing and general
decline in stock biomass in the Mozambique Channel. However,
the available literature suggests that the small-scale fleets in the
Mozambique Channel region may not have implemented many
of these capacity-enhancing technologies at this point, other than
motorization and the use of synthetic fishing gear materials.
For example, in the Comoros and Mozambique, refrigeration is
restricted to only a few boats (Chacate and Mutombene, 2013;
Breuil and Grima, 2014a), and Madagascar’s fleet is largely non-
motorized and thus unlikely to have widespread refrigeration.
Such technological advances do result in effective effort growth of
fleets over time even when the number and size of vessels remains
the same, and would need to be accounted for in long time series
comparisons (Palomares and Pauly, 2019;Scherrer and Galbraith,
2020). Due to the general absence, for the time being, of major
technological advances in the small-scale fleets considered here,
other than motorization and synthetic materials, the present
study did not include any adjustment factors for technology creep
(Palomares and Pauly, 2019;Scherrer and Galbraith, 2020).
A limitation of the approach used by us is the assumption of
equal capacity and predictive ability of vessel length to estimate
effective fishing effort between gears; this may not always be
reflective of reality. For example, while vessel characteristics such
as length and engine power alone may predict effective fishing
effort well for some gears, e.g., for industrial trawlers (which were
not evaluated here), effective fishing effort for vessels using, e.g.,
longlines is more often dependent on the length and number
of longlines deployed and the number of hooks used per line
rather than vessel length or engine power alone (Bell et al., 2017).
Furthermore, for estimating overall effort for longline fishing,
one will need to include the effective effort (in kWday) of the
vessels which caught the bait used by the longline vessels, which
is most likely proportional to the number of hooks used overall
across all sets. Until recently, it was deemed not viable to estimate
cumulative effective fishing effort of all gears and fleets across all
countries, as standardized global conversions between different
traditional measures of effective fishing effort were lacking.
Fortunately, this has now been addressed via the standardization
of fishing effort as kWday, as shown here and in other recent
examples (Piroddi et al., 2015;Belhabib et al., 2018;Greer et al.,
2019a,b). Fundamentally, in order to catch fish, one needs an
input of energy. Prior to motorization, this energy was derived
through human power (e.g., oars) or wind-power, which in our
study was approximated through a human-power equivalent.
Since motorization, most of this energy is derived from fuel,
which has become the most expensive input in fishing. Therefore,
using kWday as the key fishing effort measure for all gears is
reasonable, and also provides an immediate indication of the
fishing cost. Expressing the returns (i.e., CPUE) in kg·kWday−1
allows easy and standardized comparison and visualization across
gears, fleets, countries, and time periods. The direct connection
between this measure of effort and fuel use, and hence fuel cost as
well as CO2emissions, also allows fishing effort and CPUE to be
readily re-expressed in economic and climate impact terms, such
as kg·$−1of fuel cost and tCO2per unit effort or unit catch.
Here, data from boats using various different gear types were
used to estimate effort from length and engine power, and as such
the kW per vessel predicted by length is thought to represent
the average vessel capacity. Because small-scale fisheries often
may switch between various fishing gears, and motorized small-
scale vessels most commonly use outboard motors with lower
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Zeller et al. Mozambique Channel CPUE and Effort
engine power (kW) than other types of motorization, the impact
of gear type on average vessel capacity is not expected to greatly
impact our results.
Infrequent and incomplete data on boat types and lengths
were commonplace in our study, and fishers who do not use
vessels, particularly women (Harper et al., 2013, 2017, 2020),
are often not considered at all in many countries’ data and
information sources (Hauzer et al., 2013). Women fishers are
frequently underrepresented in fisheries statistics and policy
(Harper et al., 2013, 2017, 2020). Many traditional perspectives
of what constitute “fisheries” and “fishers” tend to exclude or
downplay small-scale activities such as collection of seafood
from shore (gleaning) from the definition of fishing, when
in reality there is a long tradition of women and children
collecting seafood from shores in Mozambique Channel coastal
communities (e.g., Hauzer et al., 2013) and elsewhere (Harper
et al., 2013, 2020). We have accounted for the contributions of
shore-based fishers in this study as best as possible based on
available information. This is particularly important as shore-
based fishing may represent the major source of protein and
micro-nutrients to the poorest sectors of coastal communities
(Golden et al., 2016;Hicks et al., 2019;Pauly, 2019), which may
not have access to boats or elaborate fishing gear. A greater
emphasis should be given by governments’ fisheries departments
and by the scientific community to the recording, estimating
and inclusion of all small-scale fisheries in studies and data
to evaluate the impact, the food security and nutrient security
as well as livelihood importance of these fisheries as a whole
(Vianna et al., 2020).
This study focused on the small-scale fisheries in the
Mozambique Channel region of East Africa only, and did
not account for recreational or large-scale, industrial fisheries,
whether domestic or foreign. Resource overlap between the
small- and large-scale sectors is nearly global in its occurrence
and constitutes a growing source of conflict in many regions
(Le Manach et al., 2012b;Belhabib et al., 2014). Small-scale
and industrial fishers both often target similar species, e.g.,
tuna and tuna-like species in the Comoros (Breuil and Grima,
2014a), or shrimp in Madagascar (Cripps, 2009), as well as likely
elsewhere. Such resource competition, if not strictly controlled
and managed, will continue to increase the political and socio-
economic marginalization of small-scale sectors (Pauly, 2006).
African countries are also particularly vulnerable to illegal
and unregulated foreign fishing (Kurien and López Ríos, 2013).
The waters of Comoros, Mozambique, and Madagascar have
all been targeted by Asian tuna longline fleets with and
without prior access agreements (Anon, 1995;Cox, 2012;Breuil
and Grima, 2014a,b). When agreements do exist for foreign
fleets, monitoring, compliance and enforcement is difficult
and generally very limited or widely absent, and the catch is
often not landed or processed in the host country (UNCTAD,
2017). For example, tuna caught by European Union vessels
in Comoros waters are not landed in the Comoros, nor are
there fully trained onboard observers from the Comoros aboard
these vessels, despite it having been shown that full observer
coverage is necessary for equitable resource use (Zeller et al.,
2011). Thus, the foreign tuna fisheries in the Comoros does
not create any employment or livelihood support for the local
population, despite the agreement between the European Union
and Comoros being fair and transparent, and the access fees
collected promoting modernization of the domestic fishing sector
(UNCTAD, 2017). On the other hand, while European Union
fishing quotas in Madagascar had increased by 30% between 1986
and 2010, the fees paid by the European Union to Madagascar
had decreased by 20% (Le Manach et al., 2013). Governments in
this region have historically lacked the organizational structures
and resources to engage effectively in fisheries governance (Cox,
2012), in part due to decades of political instability. Considering
the often-overlooked importance of small-scale fisheries to
domestic livelihoods and food security in coastal communities,
the countries and territories in the Mozambique Channel region
may want to carefully consider the interaction between domestic
and foreign fisheries when renewing or establishing future
fishing agreements.
Given the considerable increases in effective fishing effort
observed here for small-scale fisheries in the Mozambique
Channel region, it is not surprising that the CPUE has been
declining substantially for decades now. The findings of this study
are consistent with previous suggestions by Watson et al. (2013)
who, based on a shorter time series (1950–2006), suggested
that CPUE had been declining globally since 1950, including
in the Indian Ocean. Declining CPUE trends in the absence of
effective effort restrictions generally are indicators of declining
relative abundance of fished stocks (Hoggarth, 2006). Given the
country-level focus in the present study, it is challenging to
draw specific conclusions on the status of any particular stock
or species, but the overall declining CPUE in all EEZs points to
serious concerns about the status of the fish stocks underlying
and supporting small-scale fisheries in the Mozambique Channel
region, as it does elsewhere in the western Indian Ocean (Christ
et al., 2020). We suggest that this decline in CPUE should
be viewed as a serious warning sign of decreased abundance
and biomass of the exploited fish populations. Thus, local
governments should consider implementing policies to promote
recovery of fish populations, i.e., stock rebuilding, to abundance
levels that readily support maximum sustainable yields (Pauly
and Froese, 2020). This will require minimizing or restricting
further growth in fishing effort until the biomass and abundance
of local stocks can recover. Enforcing gear restrictions (e.g.,
larger mesh and hook sizes) and permanent no-take zones would
assist in rebuilding fish populations. Such effort and spatial
access restrictions should also apply to foreign fleets due to the
limited direct local benefits provided and possible interaction and
conflict with domestic small-scale fisheries. Given the importance
of small-scale fisheries in the Mozambique Channel, the adoption
and enforcement of such policies could result in considerable
improvements in food and nutrient security as well as the socio-
economic condition of coastal communities in the region.
DATA AVAILABILITY STATEMENT
The raw data supporting the conclusions of this article will be
made available by the authors, without undue reservation.
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Zeller et al. Mozambique Channel CPUE and Effort
AUTHOR CONTRIBUTIONS
DZ developed and formalized the fisheries data reconstruction
approach and conceptualized, drafted, revised, and edited the
manuscript. DZ, MP, and DP conceptualized the development
of the fishing effort data reconstruction, developed the
methodological approach, and conceptualized, edited, and
revised the manuscript. MA assembled catch data and
reconstructed effort data, synthesized CPUE data, prepared
the figures and Supplementary Material, and drafted, revised,
and edited the manuscript. KG advised on effort reconstruction
methods. AC, BD, GV, and S-LN contributed to the effort data
reconstruction, assembled catch data, and edited the manuscript.
AZ collected and reconstructed fishing effort data and edited the
manuscript. All authors contributed to the article and approved
the submitted version.
FUNDING
All Sea Around Us and Sea Around Us –Indian Ocean research
is supported by the Oak Foundation, the Marisla Foundation,
the Paul M. Angell Family Foundation, the David and Lucile
Packard Foundation, the Minderoo Foundation, and Bloomberg
Philanthropies via Rare.
ACKNOWLEDGMENTS
This is a contribution of the Sea Around Us –Indian Ocean
and the Sea Around Us, at the University of Western Australia
and the University of British Columbia, respectively. We thank
numerous colleagues and all current and former Sea Around
Us staff, students and volunteers for assistance over the years
in assembling the gradually evolving catch and effort datasets.
We thank Elaine Chu for preparing Figure 1. All errors that
remain in the presented data are ours, and we appreciate errors
and oversights, as well as new data sources being pointed out to
us for correction.
SUPPLEMENTARY MATERIAL
The Supplementary Material for this article can be found
online at: https://www.frontiersin.org/articles/10.3389/fmars.
2021.707999/full#supplementary-material
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