Marine Mammal Bycatch in New England – A Research Paper


Marine Mammal Bycatch in New England 

Written by Lex P. – Spring 2020 Marine Animal Rehabilitation & Environmental Education Intern

Fishing and seafood consumption has been increasing globally at an alarming rate. According to NOAA, American fisheries landed 9.9 billion pounds of fish and shellfish and imported 5.9  billion pounds more in 2017 alone. While eating more fish has long been praised by health care professionals for its human health benefits, fishing has serious ecological implications in the form of bycatch. 

Bycatch includes all unwanted fish or other marine animals that are incidentally caught or killed during commercial fishing. Animals can suffer severe wounds from entanglement in the nets, and air-breathing animals such as marine mammals and sea-birds can easily suffocate or drown.  Even discarded, unused fishing gear, often called ghost nets, can entangle and drown marine life as it drifts through the ocean.  

A global review in 1991 found that incidental mortality in passive fishing gear, gear that is left in place for an extended period before retrieval, has contributed to the decline of several pinniped species and populations. An updated review that compared these past results to more recent findings in 2013 concluded that 66% of pinnipeds, along with 75% of odontocets, 64% of mysticetes, and 100% of sirenians and marine mustelids were recorded as gillnet bycatch in the 20 years preceding the study. (Reeves, et. al 2013)  

The review also compares recent studies to the results of the 1990 Symposium and Workshop on the Mortality of Cetaceans in Passive Fishing Nets and Traps in order to see which species have declined. The results were troubling: the species in which bycatch levels were not reduced since 1990 are almost all either failing or extinct (Reeves, et. al 2013). Thus, it is clear that bycatch is still a very pressing issue that threatens ecosystems and population diversity and health.  

A summary of marine mammal bycatch estimates in New England sheds light on the specific species that are being caught as bycatch in this area. The study focuses on the sink gillnet fishery between 1993 and 1996. The study uncovered that harbor porpoises, white-sided dolphins, commondolphins, harbor seals, gray seals, and harp seals were all incidentally caught by the Northeast sink gillnet fishery in 1996. The paper further segregates these species into two groups: strategic and nonstrategic species. A species is considered strategic if the total fisheries bycatch is greater than the Potential Biological Removal Rate (PBR). (Bisack 2003). According to NOAA, the Potential Biological Removal Rate is defined as is defined as the maximum number of animals, not including natural mortalities, that may be removed from a marine mammal stock while allowing that stock to reach or maintain its optimum sustainable population. Thus, the harbor porpoise and the common dolphin, both of which were listed as strategic stock, were being removed from their environment at an unsustainable rate that, if continued, would inevitably lead to the decline of the population. 

Bycatch levels are a difficult parameter to study, due to an incentive on fisheries to over or under report. While it is difficult to study just exactly how much marine mammal bycatch is occurring, it is abundantly clear that bycatch can be a serious issue for marine mammal populations. While the Marine Mammal Protection Act has helped to call attention to and regulate bycatch, it is still imperative that we strive to reduce it through increased study, regulations, and ethical consumption. 



Bisack, K. D. (2003). Estimates of Marine Mammal Bycatch in the Northeast (New England)Multispecies Sink Gillnet Fishery in 1996. Northeast Fisheries Science Center Reference Documents. 

Reeves, R. R., McClellan, K., & Werner, T. B. (2013). Marine mammal bycatch in gillnet and other entangling net fisheries, 1990 to 2011. Endangered Species Research, 20, 71–97. doi: 10.3354/esr00481