Climate change is impacting marine species, populations, ecosystems, and the fisheries and communities they support. While there is broad agreement that climate change should be considered when assessing the status of exploited stocks and making harvest decisions, there is little consensus on how to do so. This study aims to increase knowledge and awareness of climate change and its impacts on fisheries and ecosystems across the Northwest Atlantic Fisheries Organization (NAFO) Convention Area, following NAFO’s 2023 resolution to address the effects of climate change on NAFO fisheries and to provide guidance on adaptation and mitigation in support of climate-resilient fisheries. A comprehensive literature review was undertaken, supplemented by analyses of projected climate change and its ecological impacts across the NAFO Convention Area. Various climate changes are observed and projected, including surface and bottom warming, deoxygenation, acidification, reduced sea ice, and altered mixing and nutrient flux. These climate changes are associated with a range of ecological shifts, including altered productivity and mortality rates, geographic range shifts toward more northerly and/or deeper waters, earlier ages at maturity but reduced body sizes, shifted phenology, and trophic mismatches, with disproportionate impacts on high-trophic species. Half of the species examined in the NAFO Convention Area are at high risk of being adversely affected by anthropogenic climate change over the next 75 years. In many areas, climate impacts on fisheries living resources are already occurring or are projected within the next few decades. However, a notable lack of information on climate change impacts was observed for some species, leading to uncertainty in climate risk assessments. Interpreting these findings within the NAFO fisheries management context and in light of its ecosystem approach to fisheries roadmap, several approaches to addressing the impacts of climate change on NAFO fisheries are discussed.
Novel acoustic receiver applications have recently enabled the monitoring of movements of migratory oceanic species. One such species is the Atlantic Halibut, a commercially important deep-water flatfish that exhibits complex migratory behaviours throughout the Northwest Atlantic Ocean. Here we set up a 144 km2 receiver grid (n = 24 VR4 receivers) in an important halibut hotspot on the Scotian Shelf and tagged 245 halibut with V13 and V16 tags from 2020–22. Receiver performance was assessed using a Receiver Efficiency Index, indicating that the deeper eastern side of the array was an area of high relative importance for future receiver deployments. Many halibut remained in consistent, localized areas over several years, occasionally making short movements into deeper water. We were also able to assess the post-release behaviour of four recaptured pre-tagged halibut within the grid array, indicating a brief period of hyperactivity and an eventual return to their previously observed behaviours. Wave gliders surveyed the grid site annually from 2021–23 to compare the efficacy of active tracking to stationary arrays for future halibut telemetry projects. Two of three tracking missions were disrupted by environmental disturbances, but results from the 2023 tracking mission indicated that the glider was able to detect more individual halibut than the stationary array in the same time frame. However, the short duration of the glider missions precluded their ability to identify movement and migratory patterns. Here we report lessons learned to streamline future project design for open ocean telemetry and halibut acoustic tracking.
Little literature exists on green crab (Carcinus maenas) and particularly rock crab (Cancer irroratus) in Newfoundland (Canada) waters. In this study, we document demographic composition for the two species upon invasion of green crab into the North Harbour, St. Mary’s Bay, estuary, an area previously only occupied by rock crab and undergoing progressive warming. Using data collected via a citizens science approach, we address objectives of documenting the rate of change in speciation upon green crab invasion in the estuary and providing novel data on basic life history processes for rock crab and green crab in Newfoundland waters. The study shows a rapid proportional switch in species composition in the estuary upon green crab invasion, with green crab increasing from a proportion of 0 to 0.75 of collected samples within three years of being detected. Novel data on rock crab suggest overall consistencies with life history processes as described in the broader literature, including presence of molting periods centred near May and August, a shallow water mating migration in fall, and a similar size-at-instar structure as crab along the eastern United States. Novel data on green crab biology suggests the St. Mary’s Bay population has similar life history attributes as the original invading population in Newfoundland, including spring-summer spawning and an inferred paucity of molting in fall. Allometric carapace relationships of the North Harbour green crab are the same as those described in the Pacific and northeast Atlantic oceans. The size structure of green crab in the North Harbour estuary has broadened in the three years since initial detection with increased presence of large crab beyond the supposed size-at-maturity in recent years.
Georges Bank is a shallow plateau off the coast of New England that has supported productive fisheries for centuries. One of these fisheries targeted yellowtail flounder (Limanda ferruginea), which at its peak caught over 21 000 mt a year. However, the stock has fluctuated, with periods of high abundance (1970s and 2000s) and low stock size (1990s and 2020s). A review published twenty years ago documented the collapse of the stock in the 1990s and subsequent recovery in the 2000s, hypothesizing the major reason for recovery was bilateral science and successfully coordinated management intervention. Unfortunately, by the time that review was published, the stock had started to decrease again and collapsed in the 2010s. We provide an updated historical review of the fishery and past stock assessments. We conduct new analyses of empirical indicators of spatial distribution and growth for Georges Bank yellowtail flounder and project the stock into the future using the most recent stock assessment. Results suggest that fishing was the likely cause of initial stock depletion while environmental changes, particularly bottom temperature, has limited recovery in recent years. Projections suggest that the population can increase in the future but its ability to increase is related to bottom temperature on Georges Bank. These results give insight into the dynamics an iconic New England fishery and stock, as well as, provide a unique opportunity to study the fluctuations of a stock through multiple periods of recovery and collapse.
Electronic monitoring (EM) systems are tools that can generate fisheries survey data when at-sea challenges such as on-deck logistics, workload capacity, or deployment interruptions prevent staff from fulfilling their duties. We sought to validate EM’s specific utility in collecting fish lengths at a comparable resolution to those collected at sea during a fishery-independent survey, the Gulf of Maine Bottom Longline Survey. We also examined whether measurement accuracy was influenced by tail morphology and length type (fork, total, and stretched total) by selecting individuals from six anatomically variable species. Individuals were measured twice: Survey-based length measurements, LS, were recorded using an electronic measuring board and EM-based length measurements, LE, were visually estimated using a color-coded EM measuring strip during video review. Paired Wilcoxon signed rank tests determined significant differences between the LS and LE distributions for all species overall, and for individual species Atlantic cod, cusk, haddock, and spiny dogfish but not thorny skate or white hake. Kolmogorov-Smirnov tests detected no difference between the distributions of LS and LE, overall and for each species. Examination of the differences between LS and LE for every individual, LD, indicated that the EM-based method slightly over-estimated lengths (μ = 0.89 mm). Linear regression indicated that the effect of extreme small or great lengths on absolute LD was present only for Atlantic cod where LD increased as fish length decreased. Pairwise comparisons of LD among fish length types indicated that fork and stretched total length measurements were overestimated by the EM-based method (μ = 2.39 mm, 3.09 mm, respectively) and this was significantly more than total length (μ = 0.04 mm). We demonstrated that collection of fish lengths using video review could be an adequate substitution for collecting lengths by hand, though it is at the discretion of the end users to determine whether these length differences exceed the acceptable range. These results have particular applications to small scale survey operations, research, and the fishery-dependent sector.
Changes in Atlantic cod (Gadus morhua) abundance at Flemish Cap, likely due to exploitation and perhaps also to changing environmental conditions, have been well documented since 1980s. While the ecological implications of cod fluctuations have been explored in relation to dominant and commercially important species including redfish (Sebastes spp.), northern shrimp (Pandalus borealis) and Greenland halibut (Reinhardtius hippoglossoides), the broader ecological impacts, e.g. on less abundant species, remain less well explored. This study aimed to analyse spatiotemporal variation in the distribution and abundance of cod, and identify associated changes in distribution and abundance of other species with various trophic relationships to cod. This analysis used a delta Generalized Additive Model (GAM) approach, incorporating binomial and quasi-Poisson GAMs fitted to EU bottom trawl survey data from 1993 to 2019. Trophic species and guilds were defined based on the sizes and feeding habits of each species, as established in previous studies. Atlantic cod is considered to comprise of two trophic species: cod under 46 cm and larger cod. Model predictions were used to construct distribution maps and estimate distribution range and annual total abundance. Bottom temperature was a more important predictor in abundance (quasi-Poisson) models than in presence (binomial) models. The observed decline in cod abundance was associated with contraction in the distribution range. Significant negative correlations were identified between cod trophic species and all but one of the other trophic species in the same trophic guilds, for both distribution range and abundance. Species in other trophic guilds that rely on northern shrimp as prey also exhibited negative correlations with cod. The abundances of the main prey of cod, namely juvenile redfish and northern shrimp, showed negative correlations with cod abundance but no relationship was seen for distribution range. The abundance of large Acadian redfish (S. fasciatus) and large beaked redfish (S. mentella), which are major prey species of cod, was positively correlated with that of large cod, suggesting that the abundance of these prey species depends more on external variables, such as intense exploitation, than on their predator-prey relationships. These findings highlight the importance, for fishery management, of considering both the direct effects of fishing mortality and the indirect effects via trophic relationships.
We present a synthesis of all sampling programs aimed at collection of ichthyoplankton conducted in coastal waters of eastern Newfoundland during the period 1982–2016, describing seasonal patterns in the succession of 22 taxa in terms of diversity, probability of occurrence, and overall abundance. Additionally, we assess whether changes in these patterns occurred prior to and after the collapse of major commercial fish stocks and accompanying shifts in ecosystem structure. Despite differences in relative species composition and community structure among bays, we identified clear and repeatable patterns in the seasonal cycle of species succession from Placentia Bay, on the south coast, to White Bay on the northeastern coast of the island. Some of the differences among bays reflected latitudinal patterns in the timing of the seasonal environmental cycle, with increasing delays toward northerly bays. Relatively few species generally dominated the larval fish community, although dominance varied seasonally, particularly once emergence of capelin commenced in July and August. Abundance of larval fish reflected the changes in abundance of adult stocks of commercial species, with strong declines in density following stock collapses, but larval decreases extended to non-commercial coastal taxa potentially removed as bycatch or through impacts of changes in ocean conditions that contributed to the decline of major ecosystem stocks (e.g., Atlantic cod, capelin, American plaice). Although differences in timing and extent of ichthyoplankton collections confounded our data, the general consistency of our observations with other sources of information (e.g., research vessel trawl surveys) highlights the value of such collections to monitoring of areas poorly represented by other types of surveys. Knowledge of changes in larval fish community structure in coastal areas can set a foundation to understand better the potential interaction between anthropogenic and climate impacts on the ecosystem state in coastal areas.
The daubed shanny (Leptoclinus maculatus) is an Arctic-boreal fish species with a circumpolar distribution and whose southernmost extent of its range in the northwest Atlantic is the Gulf of Maine. Because life history characteristics of fishes often vary along latitudinal gradients, the daubed shanny population in the Gulf of Maine may exhibit different biological characteristics and population dynamics than the Arctic populations from which most information about the species comes. To improve our knowledge, this study was undertaken to document trends in temporal abundance, spatial abundance, and depth and temperature ranges based on historical trawl surveys, and to evaluate sex-specific differences in size, weight and age of individuals captured in the Gulf of Maine. The species was distributed throughout the western Gulf of Maine, primarily at depths from 30 to 120 m in spring and in waters ≥82 m in fall and was associated with the near-lowest temperatures available in the survey regions. Most daubed shanny were ≥8–9 cm total length in spring, but small fish (7–11 cm total length) dominated catches in fall, possibly representing pelagic post-larvae settling to the benthos. The population abundance of daubed shanny fluctuated widely since 1963 but appeared to collapse after 2009 in concert with warming temperatures and declines in Calanus copepod abundance in the Gulf of Maine. Female daubed shanny were larger and heavier than males, and both sexes reached a maximum age of six years. Compared to published data, daubed shanny in the Gulf of Maine has a shorter life span, grows faster and likely experiences higher natural mortality than the Svalbard, Norway, population above the Arctic circle.
Discards from commercial fisheries have been linked to detrimental effects on ecosystems and stocks of living marine resources. Understanding spatial and temporal patterns of discards may assist in devising regulatory practices and mitigation strategies and promote sustainable management policies. This study investigates data from bycatch monitoring programs using a machine learning approach. We used a gradient boosting classifier for describing catch and bycatch patterns in the U.S. Mid-Atlantic Black Seabass (Centropristis striata), Summer Flounder (Paralichthys dentatus), Scup (Stenotomus chrysops), and Longfin Squid (Doryteuthis pealeii) fisheries. We used oceanographic, biological, spatial, and fisheries data as explanatory model features. We found positive associations between target species volume and bycatch. Although we found that sea surface temperature and year were important model features, the direction of impact of those predictors was variable. From our findings, we conclude that machine learning approaches are promising in supplementing traditional methodologies, especially with the increase in data availability trends.
According to the latest estimates, the Gulf of Maine is currently warming faster than 99% of the world’s oceans. As a result, this region has become an ideal location for research into the effects that warming has on the historical fisheries that make up this ocean basin. Both white hake (Urophycis tenuis) and red hake (Urophycis chuss) are common Gulf of Maine groundfish species, distributed both inshore and offshore. While these two species are closely related phycid hakes, white hake stocks are recognized in the Gulf of Maine as rebuilding, while red hake are above target biomass levels. As a species commonly found throughout the Gulf of Maine that prefers cooler waters (4–12°C), we hypothesize the effects of climate change might influence stock behavior, such as changes in species distribution. We used generalized additive models (GAMs) to describe the relationship between hake abundance and environmental conditions using bottom temperature, bottom salinity, depth, and catch data contributed by the Maine Department of Marine Resources during their Maine – New Hampshire Inshore Trawl Surveys of the last 22 years (2000 – 2021). Our results reveal species-specific preferences for bottom temperature (white hake ~9 to ~13℃, red hake < 12℃) and depth (white hake ~55 to ~100m, red hake > ~65m), with no significant correlation to bottom salinity. Spatially over time, white hake abundance displayed a gradual center of gravity northward, while red hake rapidly increased inshore. Overall, these results highlight species-specific density changes in inshore distribution, consistent with previous studies, with considerable implications on future management strategies in this region.
We re-analyze Thorny skate data from two comparative fishing experiments conducted by DFO in 1995 and 1996 using improved and more contemporary methods to estimate the relative efficiency of the Campelen 1800 demersal shrimp trawl survey protocol compared to the Engel 145 otter trawl. We correct possible bias in the method previously applied to these data. We investigate if there are size-based differences and if depth or spatial regions have important effects on results. We also investigate the influence and robustness of the estimation procedures, which was a concern in the original analyses of these data for other groundfish species. We did not find strong evidence that the relative efficiency of the Campelen trawl protocol compared to the Engel was different for smaller-sized Thorny skate compared to larger ones. However, we conclude that there is a potential that size-based differential catchability existed but there is insufficient information to reliably estimate these effects for Thorny skate. We also found evidence of significant differences in relative efficiency among NAFO Divisions and experiments, which is similar to other flatfish species. However, the mechanisms for these differences are unknown and it is not clear if spatial estimates should be used when converting Engel indices to Campelen equivalents. Hence, we do not recommend a different Engel-Campelen conversion factor than the one currently used in stock assessments for Thorny skates on the Grand Banks (NAFO Divisions 3LNOPs).
We conducted an interdisciplinary review of available information (i.e., genetics, life-history, and movement) to evaluate the stock structure of a previously targeted shark species, the porbeagle (Lamna nasus), in the North Atlantic. Most available information supports the conclusion that porbeagle consist of a single genetic population in the North Atlantic, which is relevant for determining species conservation status. However, the observed movement rates between the Northwest, Northeast Atlantic, and the Mediterranean appear to be low enough to consider separate spatial units for stock assessment and fishery management. The review reveals different interpretations among the organizations involved with the conservation, management, and assessments of porbeagle in the North Atlantic regarding biological population and stock boundaries. Differences in the spatial definition of management units among management organizations may pose an impediment to conserving porbeagle populations and achieving management objectives. We recommend an increased collaboration between organizations involved in highly migratory shark species as it would be beneficial for data collection, data inclusiveness, the robustness of assessments, and provide clarity for fishery managers, scientists, and the public on stocks and status. This review demonstrates that the interdisciplinary approach to stock identification is particularly valuable for data-limited species because no single approach typically has enough information to be definitive. Clearly defining management units that reflect the biological populations of porbeagle in the North Atlantic is expected to reduce uncertainty in stock assessments and help achieve current management and conservation goals of rebuilding North Atlantic porbeagle stocks.
Amidst constantly changing biotic and abiotic conditions, a more thorough understanding of the ecological consequences of dynamic predator-prey interactions will likely enable increasingly sustainable fisheries management. This study assessed the diet of striped bass, a generalist marine predator in coastal Massachusetts that feed on a variety of prey species and impose top-down pressure on other important fishery species, such as the American lobster and Atlantic menhaden. We explored the role of ontogeny using both stomach content and stable isotope analyses. Empirical results from 158 striped bass collected in northern Massachusetts revealed that striped bass in this area may have shifted from feeding predominantly on Atlantic menhaden in the late 1990s and early 2000s to Atlantic mackerel in this study. Stable isotope data suggested that the diet of striped bass is significantly linked with ontogeny: larger fish feed more heavily on benthic prey, particularly in the latter half of their seasonal residency in Massachusetts. Our study suggests that large striped bass gain an energetic advantage, as indicated by a liver somatic index, by feeding on benthic prey, possibly due to decreased foraging costs. Collectively, this work illustrates the ability of predatory fish to capitalize on the variability of forage fish populations, but highlights the importance of invertebrate prey for large striped bass and proposes underlying mechanisms driving ontogenetic diet switches from piscivory to benthivory
The management of Atlantic herring in the Bay of Fundy/Gulf of Maine/Scotian Shelf region of the Northwest Atlantic (NAFO areas 4WX5YZ) assumes separate stocks in Canadian and US waters; however, herring landed in the weir fishery in southwest New Brunswick (SWNB) are assumed to be of US origin for management purposes. The present study is a review of tagging studies that have been conducted on herring since the 1950s in NAFO areas 4WX5YZ. The tagging data show consistent patterns over time. Juvenile herring in the coastal Gulf of Maine and SWNB nursery areas generally show only movements between these two areas. These nursery areas are believed to include herring that hatched from the US and Canadian spawning grounds, contrary to the current management assumption for the weir fishery in SWNB. As herring mature, they are understood to primarily return to their natal spawning area. The tagging data show mixing of adults from different spawning grounds (including transboundary mixing) during the summer feeding and overwintering seasons. Canadian spawners have been observed to overwinter in New England and US spawners have been observed to overwinter in Nova Scotia. Herring tagged on Canadian spawning grounds have been recaptured in the SWNB weir fishery, refuting the assumption that all herring landed in this fishery are of US origin. The tagging data suggest that the weir fishery comprises a mix of herring hatched from spawning grounds in Canada and the US. The biases associated with recapture data from tagging programs precludes estimation of any proportions of stock mixing. Alternative methods for evaluating stock structure in NAFO areas 4WX5YZ are recommended.
Increases in natural mortality have been suggested as a potential driver for both the collapse and lack of recovery for the American plaice (Hippoglossoides platessoides) population on the Grand Bank of Newfoundland in NAFO Divisions 3LNO. However, natural mortality is among the most difficult parameters to estimate since it can be confounded with other parameters and model misspecifications. One method used to avoid this confounding involves modeling unfished components of a population where total mortality and natural mortality are equal. Here, we use a state-space metapopulation dynamics model to investigate whether there is evidence that natural mortality rates for unfished juvenile American plaice have varied since the population collapse. In addition, our model examined the degree of synchrony in age-1 recruitment signals between each management Division. The best fitting model included temporal variability in natural mortality rates, but estimates did not frequently differ from zero. This indicates that change in natural mortality rates is not an important driver of current juvenile 3LNO American plaice stock dynamics. Instead, this model identified that juvenile stock dynamics were mainly affected by variations in age-1 recruitment. Furthermore, a correlation analysis of the temporal variations in recruitment showed that trends were somewhat dissimilar between NAFO Divisions 3L and 3NO. Overall, although increases in M have been suggested by recent studies, we did not find strong evidence for this in juvenile fish.
The data-limited nature of Atlantic halibut (Hippoglossus hippoglossus) in U.S. waters hampers evaluation of what may be a slow but steady rebuilding pattern. Here, we collaborate with the commercial fishery to design and implement a multi-gear sampling program that collected 100s of biological samples from throughout the Gulf of Maine in a five-year period, 2014–2018. Examination of sectioned otoliths revealed a maximum age of 12 years (females) and 13 years (males); in comparison, Atlantic halibut as old as 40–50 years have been collected elsewhere in the western North Atlantic. Growth modeling confirmed sexual dimorphism, with a larger asymptotic length (L∞) for females (214 cm fork length [FL]) than males (195 cm FL). Estimates of median female length at maturity, L50, of 128 cm FL (124–132 cm, 95% confidence limits), and median female age at maturity, A50, of 9.6 years old (9.0–10.8 years), were longer and older than previous reports for the Gulf of Maine, likely resulting from our use of histological instead of macroscopic methods to classify maturity. Histology demonstrated that vitellogenesis initiated in individuals in spring, nearly a year prior to spawning, which allowed us to identify first-time (primiparous) spawners and provided the first potential evidence of skip spawning for this species. Finally, an index was developed to track the proportion of potentially mature females in the fishery, which showed an increasing trend; this qualitative tool may prove useful in a data-limited environment for evaluating the relative stock status of Atlantic halibut.
Capelin (Mallotus villosus) is a key forage fish species within its circumpolar range. This species’ importance lies in its role in the typical marine ‘wasp-waist’ food web, where capelin acts as a conduit for energy flow from lower to higher trophic levels. Herein we describe a novel observation of capelin spawning subtidally on an annual brown algae species, Desmarestia viridis, during July–August 2019 in Placentia Bay, Newfoundland, Canada. Based on extensive video surveys of the seabed along with shoreline surveys and sediment sampling, we did not find other nearby sites with typical capelin subtidal and intertidal spawning habitat (i.e. medium sand to pebble gravel). Findings suggest that capelin spawned directly on this brown algae species, D. viridis. Eggs adhered to D. viridis developed normally and hatched successfully. As temperatures of intertidal areas are predicted to increase above temperatures suitable for capelin egg rearing (2–12°C) with climate change, D. viridis may become a high-quality subtidal spawning habitat for capelin and other fish species. In support, this algal species is adapted to colonize high disturbance areas, allowing protection from egg predators in a high flow environment while also being resistant to urchin grazing.
Abundance estimates are essential for fisheries management, but estimating the abundance of open populations with low recapture rates has historically been unreliable. However, by using mark-recapture data modulated with survivability parameters obtained from analysis of acoustic telemetry data, more accurate abundance estimates can be made for species that exhibit these characteristics. One such species is the Atlantic sturgeon, for which abundance estimates were designated a research priority following precipitous population declines throughout the 20th century. We addressed this research need in the Saco River Estuary (SRE), a system where the Atlantic sturgeon has been extensively studied using mark-recapture and acoustic telemetry methods since 2009. These data were analyzed using Bayesian analysis of a Lincoln-Peterson estimator, constrained with parameters from a Cormack-Jolly-Seber model, to provide an initial abundance estimate for the system. The resulting estimate indicated that approximately 3 299 (95% Credible Interval: 1 462–6 828) Atlantic sturgeon utilize the SRE yearly, suggesting that the SRE provides critical foraging habitat to a large contingent of the species within the Gulf of Maine. The present study demonstrated the method utilized herein was effective in generating a reasonable estimate of abundance in an open system where recapture events are rare, and therefore may provide a valuable technique for supplying initial estimates of fish abundance in additional systems that display similar characteristics.
Many commercial fisheries face bycatch challenges.Avoiding non-target species while maximizing harvest of target species may require fishing differently across seasons and years, so the ability to predict bycatch occurrence is important for efficient and sustainable fishing operations.We demonstrate a potential application of bycatch predictions in the Atlantic sea scallop (Placopecten magellanicus) fishery.Catch data from a bycatch survey were used to develop models for yellowtail flounder (Limanda ferruginea) bycatch in the scallop fishery in response to environmental variables, and the models were validated using at-sea observer data.Results indicate that location (latitude, longitude, management area), temperature, zenith angle (a proxy for ambient light), and temporal effects (season, month, year) affect the presence and abundance of yellowtail flounder bycatch in the scallop fishery.Simple models with a subset of variables (latitude, longitude, and month) were fitted to help predict the magnitude and location of bycatch prior to fishery openings and in areas with no bycatch information.This study demonstrates how predictive models can be used to avoid bycatch species.
