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Implementation of a multispecies model GADGET to the ecosystem of Flemish Cap and incorporation to the fisheries stock assessment of NAFO; a case study

Final Report Summary - GADCAP (Implementation of a multispecies model GADGET to the ecosystem of Flemish Cap and incorporation to the fisheries stock assessment of NAFO; a case study)

1.- Executive summary
Traditionally fisheries management has been develop under a single species approach, where interactions among species are disregarded. This has been the case also in the Northwest Atlantic Fisheries Organization (NAFO) convention area. However since the massive collapse of cod stocks in the Northwest Atlantic, and especially since early 2000s, the Ecosystem Approach to Fisheries EAF management approach is being promoted, which was finally stated with the formation of the Working Group for Ecosystem Studies and Assessment (WGESA). One of the main topics in the roadmap of the WGESA is the development of multispecies models that are planned as one of the key elements in the management framework devised by the scientific council of NAFO for an EAF.
The Flemish Cap is a deep water mountain, with a high degree of isolation (minor migrations), and relative simplicity. Cod, redfish and shrimp are very important commercial species with strong trophic interactions that influence in population dynamic and interact with fishing activity. Hence, the Flemish Cap is an ideal case study to develop the first multispecies model in the NAFO area. GadCap deals with the development a Gadget multispecies model including cod, redfish, shrimp and their interactions with fishing activity, which will be integrated in the roadmap of the NAFO WGESA and the scientific council.
This project has been developed under the supervision of Daniel Howell, from the Institute of Marine Research of Norway, but also with the tight collaboration of scientist from the Spanish Oceanographic Institute (IEO) and the Institute of Marine Research (IIM) in Vigo (Spain), the Portuguese Institute for the Atmosphere and Sea (IPMA) in Lisbon (Portugal). These institutions have contributed with their scientific experience and the necessary data to set and develop the model. Other institutions like the Marine Research Institute of Reykjavik and the Department of Fisheries and Oceans of Canada has also contributed in the development of GadCap.
For the development of the multispecies model a training program has been followed, where Dr. Daniel Howell has been the main instructor. In addition, this formation has been complemented with specific training courses imparted by the International Council for the Exploration of the Sea (ICES) and the EU Joint Research Centre. Outreach activities for the general public have been accomplished through a website, spreading in newspapers, radio and television programs. Dissemination into the scientific community has been was faced trough meetings with the most important scientific working group in multispecies assessment methods (the ICES WGSAM) and the ICES Annual Science Conference. However, due to its relevance, the most important meetings have been those of the NAFO WGESA.
The resulting model has allowed quantifying the interactions between cod, redfish and shrimp in the Flemish cap, but especially their interaction with fishing activity. It has also permitted the estimation of multispecies maximum sustainable yields msMSY, a key element in the EAF. These results clearly indicate that disregarding the species interactions in the assessment of the Flemish Cap cod, redfish and shrimp would lead to serious underestimates of both the magnitude and the variability of natural mortality. This would involve an overestimation of the exploitable biomass in the short-term projections supporting management decisions, both by an excessive positivism in relation to the future survival of successful recruitments and the overestimation of survivorship for the fishable part of the stock. Meanwhile, it has been also shown that due to the prey-predator size relationship and the dynamic of prey-predator stock populations induced by variable recruitment, trophic interactions have a high degree of plasticity and are beyond of being only species interactions but size-modulated specific interactions. This should be seriously considered when evaluating the effect of a predator on a prey stock, otherwise the assessment of predation mortality could be misleading. In the same way, the multispecies model developed in this work presents a very suitable tool not just to understand the importance of predation, fishing and recruitment as drivers in the dynamic of the Flemish Cap system but also to quantify the shape and magnitude of species interactions as well as synergies among drivers, which could be used to support the stock assessment in the Flemish Cap.
The successful development of GadCap has opened new possibilities to continue with the development of the EAF in NAFO. Due to the capacity of this multispecies model to simulate complex interactions and feedbacks between the modeled stocks, it appears as an ideal operative model to be used for risk analysis in a management strategy evaluation framework for the Flemish Cap, and new projects are been developed in this line.
2.- Summary description of project context and objectives
Traditional approaches to fisheries management consider species as independent populations and are managed under this vision, i.e. from a single species approach. However, it has been proved that juveniles of many fish species support an intense predation rate, which may result in overestimates of stock-biomass per recruit by the single species models. This may favour declines in population or even the collapse of the stock, which could not being predicted by single-species models. Since 1950´s worldwide collapse of several marine stocks worldwide as result of an increasing fishing pressure raised the awareness about the limitation of resources and the increasing need of improving and applying a ecological knowledge to fisheries management. The massive collapse of all the Northwest Atlantic cod Gadus morhua stocks since 1990, including the Flemish Cap cod stock (Figure 1 - see Attached Final Report) triggered the change of fisheries management toward a precautionary approach, with higher multispecies and ecosystem considerations.
Historically, since the discovery of North America in 1497, the Northwest Atlantic cod stocks, highly abundant in these waters, became of extreme importance for European fleets. Since 1960, when declared catches information started to be collected, until 1978 when the Canadian Exclusive Economic Zone (EEZ) was established, total landings by the European fleet averaged 1 million tons, 70% of which was cod. Since 1978 foreign fleets were confined to ground fishes located out of the EEZ, among them the Flemish Cap (Figure 1). During these years catches were mostly constituted by cod and redfish Sebastes sp. until the massive collapse of all Northwest Atlantic cod stocks in the early 1990’s. Since then, fishing was mostly focused on Greenland halibut Reinhardtius hippoglossoides and Northern shrimp Pandalus borealis.

Since 1949, the Northwest Atlantic Fisheries Organization (NAFO, originally ICNAF) is in charge of the rational management and conservation of most fishery resources in the Northwest Atlantic, with the EU as one of the main contracting parties. Up to date, exploited species are managed under a single species approach in NAFO. However in 2008 the NAFO Working group for Ecosystem Studies and Assessment (WGESA) was created with the mission of providing advice in issues like Vulnerable Marine Ecosystems, fisheries production potential, eco-regions delimitations and very importantly, the influence of species interactions in the assessment of stock dynamic and management decisions.
The Flemish Cap is a deep water mountain located in NAFO area 3M (Figure 1). Two features provide high degree of isolation to the Flemish Cap marine populations. First, the cap is separated from the Newfoundland shelf by the Flemish Pass (Figure 1), a channel with depths beyond 1100 m. Second, a quasi-permanent anti-cyclonic gyre dominates the oceanography over the Cap producing a retention effect on eggs and larvae that would eventually stay over the Flemish Cap and recruit to the population. Species interdependence in the Flemish Cap has been just recently evaluated, and results showed a clear influence of cod predation in the dynamic of the redfish and shrimp stocks, while redfish has a strong influence in shrimp. Hence, it seems of great relevance the development of multispecies models in the Flemish Cap, evaluating the importance redfish-shrimp-cod interactions in a context of fishing activity.
The relative simplicity (85% of total biomass hoarded by cod, redfish and shrimp), the above mentioned isolation and the long and high quality data series make the Flemish Cap an ideal candidate fishing ground to start with the development of new management approaches in NAFO. The WGESA is developing an innovative roadmap where total fisheries production potential is estimated based in primary production calculations and rates of transference between trophic levels. These estimations in conjunction with multispecies and single species models will be employed to estimate Maximum Sustainable Yield (MSY) values for the different stocks under management. This approach supposes a two side estimation of MSY, taking into account bottom-up and top-down forces in the ecosystem.
GADGET (Globally applicable Area Disaggregated General Ecosystem Toolbox) is a powerful and flexible framework that has been developed to model marine ecosystems within a fisheries management and biological context. GADCAP deals with the development of a GADGET multispecies model in the Flemish Cap. As an ecosystem model it includes cod, redfish and shrimp interactions, growth rates, maturation, mortality rates, space occupancy and recruitment variability. As a fisheries model with management aims it includes information about fleet, gear types, total catches, age and size distribution of catches by species.