Graham D. Sherwood

• Doctor of Philosophy
• Researcher at Gulf of Maine Research Institute

The spatial distribution of the Atlantic cod ( Gadus morhua ) stock is shaped in part by several habitat and oceanographic variables. In this study, Vector Autoregressive Spatio-Temporal (VAST) models were used to combine data from multiple survey programs to hindcast seasonal spatial densities of three size classes of cod within the Northeast US C...

Sympatric populations of Atlantic cod with distinct spawning times in winter and spring have been identified within the Gulf of Maine. A new western Gulf of Maine stock assessment unit in U.S. waters lumps winter and spring spawning populations into a single stock unit and future monitoring and assessment of their abundance will require mixed stock...

The warming of the world’s oceans has resulted in the redistribution of many marine species globally. As species undergo range shifts, the expanding edge of the population often experiences novel environmental and demographic conditions that may result in the emergence of variation in life-history strategies. The northern stock of black sea bass, C...

Atlantic cod (Gadus morhua) populations in the Gulf of Maine (GoM) are at a fraction of their historical abundance, creating economic hardships for fishermen and putting at risk the genetic diversity of the remaining populations. An understanding of the biocomplexity among GoM populations will allow for adaptive genetic diversity to be conserved to...

The study of the diet and feeding of cod, the methods and strategies by which cod find food, how such food is utilized, and how such resulting cod growth impacts other components of marine ecosystems is valuable. Cod have a long history as linchpins in the trophic ecology of marine ecosystems. This chapter evaluates the trophodynamics, growth, and...

We assessed annual growth of Coregonus clupeaformis (Lake Whitefish) from a natural, lightly exploited population in a small lake in northern Maine using observed and back-calculated length-at-age data. We sampled Lake Whitefish from Clear Lake, ME, with gill nets and extracted otoliths from 57 fish. We incorporated age-at-length data into a von Be...

Large predatory fishes, capable of traveling great distances, can facilitate energy flow linkages among spatially separated habitat patches via extended foraging behaviors over expansive areas. Here, we tested this concept by tracking the movement of a large mobile estuarine fish, red drum (Sciaenops ocellatus). Specifically, we addressed the follo...

Life-history strategies often vary within motile marine species, affecting morphometry, growth, diet, and fecundity. Atlantic cod (Gadus morhua) in the Gulf of Maine display marked variation in a number of life-history traits, exemplified by differences in body colour. Migratory behaviours are suspected to differ among these colour types, but have...

This report outlines the results of a 5-year acoustic survey of Atlantic herring (Clupea harengus) in Area 1A (Maine coastal portion) during the spawning season (August – November; 2012-2016). The first 2 years of this survey were supported by separate grants from the Cooperative Institutes for the North Atlantic Region (CINAR, NOAA funded) and the...

Life-history strategies often vary within motile marine species, affecting morphometry, growth, diet, and fecundity. Atlantic cod (Gadus morhua) in the Gulf of Maine display marked variation in a number of life-history traits, exemplified by differences in body colour. Migratory behaviours are suspected to differ among these colour types, but have...

Abiotic conditions greatly influence the distribution and abundance of marine organisms during early life-history phases. For instance, factors such as habitat heterogeneity often affect the dispersive phase of marine fishes, and then diminish in importance as species approach maturity and are influenced more so by biological processes. While recen...

In recent years, the abundance of American lobster Homarus americanus stocks has increased exponentially in coastal Maine, which is likely due to increased recruitment, enhanced growth rates, and decreased predation. This study analyzed the effects of lobster size (12-19.9, 20-29.9, and 30-39.9 mm carapace length, CL) and temperature on growth rate...

The decline of the Atlantic cod, Gadus morhua, stock in the Gulf of Maine to a historically low biomass has been coupled with a severe contraction in spatial range. The stock is now largely concentrated in the western Gulf of Maine. This erosion of spatial stock structure may be a factor-inhibiting recovery of Gulf of Maine cod. However, recent eff...

We describe a unique survey method that is able to cover a wide spatial and temporal range at a low cost. We utilised 10 individual small fishing vessels (lobster vessels) as acoustic research platforms to systematically survey a coastal population of Atlantic herring (Clupea harengus) in the Gulf of Maine. We examined 38 transects spanning more th...

From 1994 to 2002, five major year-round closed areas were established in the Gulf of Maine and on Georges Bank to promote recovery of groundfish species, including Atlantic cod (Gadus morhua). Here, we present life-history data for cod sampled within and next to four of the five closed areas to test the hypothesis that closed areas benefit cod. We...

Several studies have documented fish populations changing in response to long-term warming. Over the past decade, sea surface temperatures in the Gulf of Maine increased faster than 99% of the global ocean. The warming, which was related to a northward shift in the Gulf Stream and to changes in the Atlantic Multidecadal Oscillation and Pacific Deca...

Preserving larger fish is often advocated as a conservation measure to help fish populations buffer environmental variation and fishing pressure. The rationale is that several size- and age-dependent reproductive traits confer a higher reproductive value to larger fish. The effects of variation in these reproductive traits on the dynamics of popula...

Many mobile marine species are presumed to utilize a broad spectrum of habitats, but this seemingly generalist life history may arise from conspecifics specializing on distinct habitat alternatives to exploit foraging, resting/refuge, or reproductive opportunities. We acoustically tagged 34 red drum, and mapped sand, seagrass, marsh, or oyster (acr...

Diversity within populations not recognized or represented in management may lead to reductions in productivity and to population collapse. Within Atlantic cod Gadus morhua populations, physically distinct morphotypes coexist in close proximity, but their importance to population structure remains unclear. We conducted 2 acoustic telemetry studies...

Atlantic bluefin tuna (Thunnus thynnus) are currently managed as two separate stocks separated at 45W. Assessment models utilize growth curves constructed from dorsal spines in the eastern Atlantic and a combination of otoliths and modal size data in the western Atlantic. Interpreting these structures can be problematic due to low visual clarity of...

Monkfish is one of the most highly valued finfish fishery species in the northeastern United States, yet very little is known about its basic biology including growth which is currently assumed to be linear based on age results from vertebrae. Here, we present tagging and otolith data that call into question linear growth and rather support a more...

Growth of Atlantic bluefin tuna has been studied for more than fifty years in both the eastern and western Atlantic. Age estimates have been generated using a variety of different structures and protocols resulting in a set of growth parameters with a high variance. Asymptotic length, for example, ranges from 266cm to 455cm. We hypothesize a large...

American lobster (Homarus americanus) landings have more than quadrupled in the last two decades (1990–2010), coinciding with the collapse of Gulf of Maine groundfish fisheries such as Atlantic cod (Gadus morhua). Recently there has been speculation that the release of lobster from predatory control may have resulted in both lower predation rates a...

The food and feeding habits of Northern Wolffish (Anarhichas denticulatus), Spotted Wolffish (A. minor), and Atlantic Wolffish (A. lupus) in Newfoundland and Labrador continental shelf waters were examined. A total of 1,451 stomachs were analysed for contents: 152 for Northern Wolffish; 262 for Spotted Wolffish; and 1,037 for Atlantic Wolffish. No...

The reliability of population dynamics and stock assessment models hinges on accurate life-history information. Mark-recapture studies represent a commonly used technique to investigate crustacean growth, mortality, and migrations. We evaluated tagging by coded microwire tags for the American lobster, Homarus americanus H. Milne Edwards, 1837, in a...

Very little is known about the consequence of human activities on the flow of energy through natural ecosystems. Here, we present a trophic-based approach to describing energy relationships in pollutant-disturbed lakes, emphasizing the importance of prey diversity in maintaining energy transfer to growing fish. Both diet and community analysis indi...

Sherwood, G. D., and Grabowski, J. H. 2010. Exploring the life-history implications of colour variation in offshore Gulf of Maine cod (Gadus morhua). – ICES Journal of Marine Science, 67: 1640–1649. The evolution of alternative life-history strategies in fish has largely been overlooked by fisheries managers, although differences in the biology of...

Humans have reduced the abundance of many large marine vertebrates, including whales, large fish, and sharks, to only a small percentage of their pre-exploitation levels. Industrial fishing and whaling also tended to preferentially harvest the largest species and largest individuals within a population. We consider the consequences of removing thes...

We put forward a combined observing and modeling strategy for evaluating effects of environmental forcing on the dynamics of spatially structured cod populations spawning in the western Gulf of Maine. Recent work indicates at least two genetically differentiated complexes in this region: a late spring spawning, coastal population centered in Ipswic...

Yellow perch (YP) are metal tolerant fish that form large populations in many metal-impacted regions across Canada. While they are able to survive and reproduce successfully in environments with water and sediment metal concentrations that are toxic to many invertebrates, perch experience a suite of direct and indirect impacts. YP were studied in a...

Atlantic cod (Gadus morhua) was studied at the Bar Haven, Placentia Bay, Newfoundland (NAFO 3Ps stock unit) spawning ground from 1996 to 2003. Lessons applicable to management of rebuilding stocks derived from these studies are reviewed: (1) cod spawn in the same area each year, but numbers and timing vary (spawning biomass varied from 2,000 to 25,...

Cod populations in Newfoundland and Labrador waters have shown differing growth, condition and recruitment since near-universal declines in these properties during the cold period of the late 1980s and early 1990s. To assess the influence of variable prey communities on these parameters, we compared cod energetics and diet in populations off Labrad...

We examined stable carbon and nitrogen isotopic signatures of 17 fish and 16 invertebrate taxa common to the Newfoundland and Labrador (NL) continental shelf food web. Particular sampling emphasis was placed on Atlantic cod (Gadus morhua) and related prey species (e.g. shrimp, Pandalus borealis, and capelin, Mallotus villosus). We found highly sign...

Metal contamination can disrupt trophic links in food webs by altering the taxonomic composition and size structure of benthic macroinvertebrate communities. Benthic macroinvertebrates and yellow perch (Perca flavescens) were collected from six lakes along a gradient of cadmium (Cd) and copper (Cu) contamination in Quebec, Canada. The two most cont...

While temperature records are available from otolith 8180 profiles in fish, interpreting changes in otolith delta(13)C remains ambiguous. We compiled a global database of published otolith delta(13)C values for 60 species representing 30 families of marine fishes. Species' mean otolith delta(13)C ranged from + 0.5 to - 8.6 parts per thousand. Among...

The objectives of this field project were to test relationships between the physiological and population status of indigenous fish and (a) ecological factors (habitat quality, food resources), (b) toxicological factors (ambient and tissue metal concentrations), and (c) metal detoxification factors (metallothionein induction and subcellular metal pa...

Large variations in the activity and scaling patterns of enzymes involved in anaerobic metabolism exist and appear to be related to species differences in the locomotory habits of fish. Here, we show how the scaling of muscle lactate dehydrogenase (LDH) activity is highly variable in fish, not only among species, but also among populations of yello...

While the flow of energy is understood to determine the growth of organisms and the productivity of ecosystems, little is known about the sublethal effect of pollutants on the energetic efficiency of wild populations. We used field estimates of fish growth coupled to in situ estimates of food consumption rates obtained from the mass balance of a gl...

The characteristic elevation of plasma cortisol levels in response to an acute stress of capture was impaired in both male and female yellow perch (Perca flavescens) from lakes contaminated by heavy metals. The impairment of the cortisol stress response was observed in fish 4+ years and older whereas the capacity to elevate plasma cortisol levels o...

Conventional wisdom in ecotoxicology predicts reductions in organismal fitness to follow from exposure-related physiological effects. This expectation may be appropriate for controlled laboratory environments, but may not necessarily reflect what is likely to take place in the wild. In an extensive review of the ecotoxicology literature, it was rev...