MARINE MAMMAL RESEARCH NEWSLETTER   |   February 2015 (Issue 12)

CRUNCHING THE NUMBERS

How much are grey seals impacting east coast fisheries?

The Atlantic cod collapse in eastern Canada represents a collective failure of fisheries management, research and the fishing fleet, which perpetuated years of unsustainable fishing. However, the role of different factors in driving Canadian cod stock trends are difficult to interpret. Rachel Neuenhoff, a PhD student at UBC, is trying to understand the biological and socioeconomic consequences of interactions between grey seals and fisheries.

Juvenile grey seal. (photo M. Hammill).

Juvenile grey seal. (photo M. Hammill).

While some researchers maintain that unchecked grey seal population growth is to blame for declining cod stocks, others find that explanation to be a dangerous oversimplification of complex trophic dynamics in a chronically unbalanced system. Although the quintessential question, “Are grey seals eating Canadian cod to extinction” has been studied, the critical gap has always been a general dearth of data on grey seal diets. In large measure, this is due to the migratory development of cod (differences in what babies are doing versus what the adults are doing) relative to the incredible geographic ranges of grey seals along Atlantic Canada. Nowhere is the grey seal-cod controversy more charged than in the southern Gulf of St. Lawrence.

Atlantic cod (photo J. Muller)

Atlantic cod (photo J. Muller)

Over the years, the grey seal-cod question has shifted from a biological investigation, to a multi-pronged problem affecting scientists, fleet employees, management, and government. This reflects the fact that cod dynamics cannot be explained without mentioning the social, economic, and political impacts of management strategy.

Several management proposals have aimed to reduce predation on cod by grey seals. The two proposals familiar to most people have come from recent senate hearing recommendations to remove grey seals and institute grey seal birth control programs on Sable Island. However, neither of these proposals have proven satisfactory solutions that can be implemented at a scale necessary to appreciably recover groundfish.

Fishing gear at Campobello Island, New Brunswick (photo L. Lockwood)

A more pressing issue, in the past decade has been reduced catches of other species as well as the financial hardships of costly interactions between fishermen and grey seals. Fishermen report that incidents between grey seals and fishing gear as well as widespread seal worm infection, have reduced the profitability of fisheries. However, cataloging these incidents is a big task and it has not been clear to date how these incidents ultimately impact the fleet.

The goals of Rachel Neuenhoff’s PhD research are interdisciplinary: The first aim is to quantitatively describe factors limiting cod in the southern Gulf of St. Lawrence from a biological standpoint. Second, Rachel is cataloging socioeconomic impacts of interactions between grey seals and fishermen. The final aim is to create a framework in which the quantitative biological variables can be better informed by the socioeconomic variables (i.e., she hopes to make the biological variables talk to the socioeconomic ones). Essentially, Rachel’s research fuses biological and socioeconomic indicators of fisheries management values using traditional risk assessment support tools. It contributes to understanding population dynamics of a collapsed fishery in the absence of fishing pressure, and explores how quantitative and social variables can be synthesized to formulate effective management strategies.

This map shows how Lobster Fishing Areas are related to one another in regards to bait raiding, gear damage, parasite infestation and the presence of grey seals. Similar shades of blue match regions that are alike. LFA 24 did not group with any other region due to overwhelming reports of gear damage, bait raiding, seal worm infestation and grey seal sightings.

This map shows how Lobster Fishing Areas are related to one another with regards to bait raiding, gear damage, parasite infestation and the presence of grey seals. Similar shades of blue match regions that are alike. LFA 24 did not group with any other region due to overwhelming reports of gear damage, bait raiding, seal worm infestation and grey seal sightings.

To this end, a cod stock assessment for the Gulf of St. Lawrence was recently conducted in which grey seal predation was directly incorporated. Given the gaps in the grey seal diet data, Rachel has run several plausible scenarios and found that the stock assessment with seal predation agreed more closely with the traditional stock assessment when grey seal diet consisted of 30% adult cod. These estimates will be projected into the future to evaluate several different grey seal management strategies (i.e., different levels of grey seal removals from the Gulf).

In addition to the models, Rachel distributed several surveys along Atlantic Canada questioning fishermen about their interactions with grey seals while fishing. She found that gear damage and time spent repairing gear were important limitations to the fleet. Reports of seal worm infections were also numerous. These interactions were most frequent in the southern Gulf, particularly along northern PEI, which is reported to be an extremely biologically rich and diverse region.

Rachel Neunhoff preparing to work.

Rachel Neuenhoff preparing to work.

The reports from fishermen coincided with high densities of grey seals and fewer seal haul outs. This suggests that grey seals in these areas actively forage for species targeted by the fishing fleet and that they probably prey on these species in the presence of the fleet to capitalize on easy food resources.

The final component of Rachel’s research is to integrate results from the stock assessment and the fleet surveys to place a value on possible management strategies. The possibilities are represented by a risk assessment framework in which stakeholders (fishermen, managers, scientists) indicate their preferences and objectives. She will then account for the uncertainty in the system as determined by the stock assessment, the fleet surveys and the desired outcomes—and will integrate the uncertainty across all possible outcomes to produce a value for each strategy for managing grey seals and cod in the Gulf of St. Lawrence.

The final product of Rachel’s research will be a tailored framework for coping with several critical data gaps currently impeding management in the Gulf of St. Lawrence. She hopes to determine which strategies will be most valuable for managing grey seals and cod. She also hopes to determine whether it is less important to explicitly manage the organisms in the system than it is to manage the objectives and expectations of the stakeholders that rely on these resources.


Rachel Neuenhoff  is a Ph.D. Candidate at UBC’s Marine Mammal Research Unit. Her research is supported by the Canadian Fisheries Research Network — a unique collaboration between academic researchers, the fishing industry, and government agencies.


Contents | Science Outreach  | From the Lab | Into the Field |  Number Crunching | This Just In