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Managing fishing operations' threat to marine mammal populations hinges on accurate bycatch estimates, often derived from fishery observer or monitoring programmes. Much global marine mammal bycatch occurs in gillnets, and observer protocols that do not include watching the haulback of gillnets may miss animals that drop out of the net. We investigated whether trips using a fish-focused observer protocol (no requirement to watch the haulback) in US northwestern Atlantic gillnet fisheries from 1994 to 2019 had different observed bycatch rates from trips under a mammal-focused observer protocol (watching the haulbacks) for grey seals (Halichoerus grypus atlantica), harbour seals (Phoca vitulina vitulina), and harbour porpoise (Phocoena phocoena phocoena). We found that observer protocol was likely to affect observed drop-out and bycatch rates. Under the fish-focused protocol, the ratio of animals removed from the net to those that fell from the net was generally higher than under the mammal-focused protocol, suggesting fish-focused observers missed bycatch that fell. Bycatch rates of animals removed from the net by fishers differed significantly between observer protocols for seals, but not for harbour porpoise, perhaps because of differences in entanglement and manner of decomposition. We estimate bycatch was underreported by 3–25% because of unobserved drop-outs on fish-focused observer protocols. [ABSTRACT FROM AUTHOR]

Copepod size and energy content are influenced by regional and seasonal variation in temperature and food conditions, with implications for planktivorous consumers such as the endangered North Atlantic right whale (Eubalaena glacialis). Historical data (1990–2020) on Calanus finmarchicus stage CV copepodite prosome length and oil sac metrics were analyzed to determine the extent of variation in individual body size and estimated lipid and energy content in five regions of the Northwest Atlantic continental shelves [Gulf of Maine (GoM), Scotian Shelf (SS), Gulf of St. Lawrence (GSL), St. Lawrence Estuary (SLE) and Newfoundland Shelf]. Large-scale spatial patterns in size and lipid content were related to latitude, indicating that C. finmarchicus CV in the GSL and SLE were historically larger in body size, and had significantly higher lipid content compared with those in the GoM and the SS. The observed patterns of C. finmarchicus CV size and lipid storage capacity suggest that regional variation in whale prey energy content can play a role in the suitability of current and future whale foraging habitats in the Northwest Atlantic, with the larger lipid-rich individuals in the GSL providing a high-quality diet compared with those in southern areas. [ABSTRACT FROM AUTHOR]

Climate change and climate variability are affecting marine mammal species and these impacts are projected to continue in the coming decades. Vulnerability assessments provide a framework for evaluating climate impacts over a broad range of species using currently available information. We conducted a trait-based climate vulnerability assessment using expert elicitation for 108 marine mammal stocks and stock groups in the western North Atlantic, Gulf of Mexico, and Caribbean Sea. Our approach combined the exposure (projected change in environmental conditions) and sensitivity (ability to tolerate and adapt to changing conditions) of marine mammal stocks to estimate vulnerability to climate change, and categorize stocks with a vulnerability index. The climate vulnerability score was very high for 44% (n = 47) of these stocks, high for 29% (n = 31), moderate for 20% (n = 22), and low for 7% (n = 8). The majority of stocks (n = 78; 72%) scored very high exposure, whereas 24% (n = 26) scored high, and 4% (n = 4) scored moderate. The sensitivity score was very high for 33% (n = 36) of these stocks, high for 18% (n = 19), moderate for 34% (n = 37), and low for 15% (n = 16). Vulnerability results were summarized for stocks in five taxonomic groups: pinnipeds (n = 4; 25% high, 75% moderate), mysticetes (n = 7; 29% very high, 57% high, 14% moderate), ziphiids (n = 8; 13% very high, 50% high, 38% moderate), delphinids (n = 84; 52% very high, 23% high, 15% moderate, 10% low), and other odontocetes (n = 5; 60% high, 40% moderate). Factors including temperature, ocean pH, and dissolved oxygen were the primary drivers of high climate exposure, with effects mediated through prey and habitat parameters. We quantified sources of uncertainty by bootstrapping vulnerability scores, conducting leave-one-out analyses of individual attributes and individual scorers, and through scoring data quality for each attribute. These results provide information for researchers, managers, and the public on marine mammal responses to climate change to enhance the development of more effective marine mammal management, restoration, and conservation activities that address current and future environmental variation and biological responses due to climate change. [ABSTRACT FROM AUTHOR]

The article investigates the data collected by the Northeast Fisheries Observer Program (NEFOP) documenting patterns in harbour porpoise bycatch rates, the compliance levels of pinger regulations and possible habituation indications in the U.S. Northeast gillnet fishery. It notes that the Harbour Porpoise Take Reduction Plan (HPTRP) separates the fishery into management areas that are either completely closed to all gillnets or closed to those that do not use pingers. It was found out that there was no observed bycatch in pingered nets using the same mesh size used in the experiment. It was found out that 87% of the tested pingers were functional during high pinger usage, while 36% were functional during low pinger usage.

We developed an estuarine index of biotic integrity to assess habitat quality in Narragansett Bay, Rhode Island. Fish were collected at 18 fixed stations with a 61-m × 3.05-m beach seine once per month in July and August from 1988 to 1999. Stations were designated high or low quality depending on the total nitrogen concentration, number of low dissolved oxygen events, extent of human disturbance, abundance of macroalgae, and presence or absence of eelgrass . We used stepwise discriminant analysis on 13 candidate metrics based on fish community data to determine those most important in distinguishing between high and low habitat categories. We then used discriminant analysis and canonical discriminant analysis with the resulting significant metrics. The six metrics that were able to discriminate between sites were the number of estuarine spawner species, proportion of killifish, number of individuals, proportion of flounder, Shannon's diversity index, and proportion of benthic-associated species. Discriminant analysis with these metrics distinguished among sites with an overall error rate of 22%. Surprisingly, when an index was calculated from the metrics, sites designated as low quality based on environmental data had the highest scores whereas high-quality sites had low scores. Degraded sites in the upper estuary may have scored high due to the availability of shallow-water refuge from predation, abundant food, and warmer water with less current. Our results indicate that upper estuaries are important to juvenile fish and are worth protecting despite apparent human impacts. Further, an index of biotic integrity may not be useful in estuaries because of their characteristically harsh environmental conditions, which result in fish communities that are dominated by tolerant species that are habitat and feeding generalists. [ABSTRACT FROM AUTHOR]