Atlantic Cod Essay

in depth analysis of the Factors causing the Commercial Collapse of Atlantic Cod
Somayeh Rasouli
Student Number: 103548472
University of Windsor, Dr. Heffner Abstraction
The commercial collapse of the Atlantic cod (Gadus morhua) in 1992 had major ecological and socioeconomic implications that prompted the government to invest in research into management models of fisheries in order to prevent other collapses and recover the lucrative cod stocks. The factors that contributed to the cod collapsed have been studied in depth over the years. In this paper literature review of multiple studies indicated overfishing was the main source of the collapse. The role of seal predation and poor recruitment on the cod collapse was also analyzed and
the results showed that although these factors exasperated the overfishing problem, they were not major contributors to the collapse. Survey results of different cod stocks showed that the recruitment from the year classes that would have comprised most of the spawners during the year of the collapse was not significantly different from previous year classes recruitment. Moreover, mortality due to seal predation was only a small contributor to the total cod mortality. Finally, it was the lack of knowledge of ocean ecosystems and the complexities involved that also contributed to the overfishing of the Atlantic cod and its subsequent collapse. Fishery conservation would benefit from further research into the inclusion of bio-complexities and ocean system dynamics into management models.
Introduction
Commercial fisheries for Atlantic cod (Gadus morhua) experienced a complete crash in the early 1990s. The collapse extended from southern Labrador to the continental shelf off eastern Nova Scotia. The abundance of the cod stocks was so low that a moratorium was set on commercial fisheries for cod stocks in 1992. Additionally, the cod fishery was an inherent part of Newfoundlanders social and cultural identity (Higgins, 2009). The fishery represented many individuals livelihood. Thus, with the collapse of the cod fishery was not only economically crippling but also detrimental culturally. The ecological and socioeconomic impacts of the collapse prompted fisheries and the Canadian government to critically evaluate the way in which commercial fisheries were managed in order to recover the cod population and prevent such dramatic declines in abundance happening in other fish species in the future. Additionally, there are numerous explanations for the commercial collapse of the cod population. These reasons range from the of climate change to the advancements in fishing technology. Moreover, human-induced climate change altered the state of the marine environment by changing the ocean temperatures. As the temperature is strongly associated to mixing patterns and stratification it affects biological components of the ecosystem, and so it is important to cod. Studies on the relationship between temperature and cod recruitment showed a gradual negative relationship between the increase in water temperatures and recruitment (Planque & Fredou, 1999). Failure to consider the affects of climate change on recruitment has been thought to contribute to the overfishing of cod (Pershing et al., 2015). To examine the significance of reduced recruitment on the fishery collapse of the Atlantic cod the study conducted by Myers et al. (1997) will be analyzed and compared to other studies conducted on the same topic. Furthermore, studies have suggested that a major cause of the fishery Atlantic cod collapse was the increased predation pressure by seals (Atkinson and Bennett, 1994). Additionally, studies have shown that the contribution of cod to the seal diet overwinter area was greater than reported (Hammill et al. 2014). To measure the degree to which seal predation contributed to the fishery cod collapse the results of the study conducted by Chassot et al. (2009) will be analyzed and compared to other papers on seal predation pressure on cod near the time the collapse occurred. Advancements in fishing technology were crucial to the overexploitation the Atlantic cod in the mid-1980s to mid-1980s (Hamilton, 2007).
The proliferation of the new technologies such as sonar guided purse seines allowed fisherman to exploit a larger area, go deeper depths than before, for a longer time. This was made the Atlantic cod population more vulnerable to overfishing since they were the main catch of the region at the time (Higgins, 2009). In order to study the significance of overfishing on the commercial collapse of the cod population the key results the various studies will again be outlined and analyzed. Therefore, in this paper, the hypothesis that poor recruitment, increased seal predation, along with overfishing played a role in the commercial collapse of the Atlantic cod stocks will be investigated along with the importance of each factors role in the collapse. The validity of the hypothesis will be measured through a literature review of previously published studies.
Results
Effect of recruitment on the collapse of Atlantic cod A study conducted by Meyers et al.
(1997), results outlined in Table 1, showed recruitment of the year classes that made up most of the spawners biomass the year the Atlantic cod collapsed weren’t that different from the long-term recruitment levels. Of the six stocks studied in the paper, southern Grand Bank, northern Gulf of St. Lawrence and Eastern Scotian Shelf displayed lower recruitment levels in the mid-1980s (Table 1). However, Labrador and north-eastern Newfoundland, and southern Gulf of St. Lawrence showed increased recruitment (Table 1). Further, spawners biomass was extremely low in all the stocks in the mid-1980s (Fig.
1). Moreover, a study on nine cod stocks showed a relationship between temperature and recruitment, that is there is a gradual change in recruitment levels in different water temperatures (Figure 3). As temperature increased, recruitment levels gradually decreased, while a decrease in temperature resulted in an increasingly higher recruitment levels (Figure 3). Similarly, recent a recent study conducted by Pershing et al. (2015) found that female cod reproductive output declined in warmer waters.