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.

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.

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

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).

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.

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.