1.- Physical environment:
Flemish Cap is an underwater mountain located in the the Northwest Atlantic Fisheries Organization regulatory area (NAFO, originally ICNAF), division 3M. It is located around 300 miles eastern of the Newfoundland Island. The Cap occupies around 17000 square miles in depths above 1460 meters; 10555 square miles are above 730 meters and 2500 square miles above 200 meters. The top of the mountain (ca 120 m), is located in the southeast and therefore the east and south slopes are much steeper and fall abruptly to the abyssal platform, beyond 4000 m. In the northern and western areas slopes are smoother, ending in the Flemish Pass (1100 m), a channel which separates the Flemish Cap from the Grand Banks of Newfoundland with 30 miles wide in the narrowest point, considering the 400 meters depth isobaths.
MapaNAFOyDetalleFlemish
The Flemish Cap is located within the regulatory area of the Northwest Atlantic Fisheries Organization (NAFO), corresponding to the Division 3M (left panel). The Flemish Pass, a channel deeper than 1100, separates the Flemish Cap from the Grand Banks of Newfoundland (panel below).
Oceanographic properties are dominated by the Labrador Current, although they are also affected by the North Atlantic current by pulses. Over the cap exists a quasi-permanent anticyclonic gyre with a key influence in the dynamic of Flemish Cap ecosystem (Colbourne and Foote 2000, Gil et al. 2004), especially for primary and secondary production, and survival of fish egg and larval stages. This system of currents is the basis for a high productivity which has a clear seasonal cycle, with the primary production bloom starting usually not earlier than April and lasting until early autumn.
Dominant pattern of currents in the Northwest Atlantic. The Labrador Current (LC) subdivides into the inner branch (IBLC) and the outer branch (OBLC) which met with the Gulf Stream (GS) in the tail of the Grand Bank (GB) forming the North Atlantic Current (NAC). The anticyclonic gyre over the Flemish Cap (FC) formed by the OBLC is also shown.
Topographic and oceanographic features produce a high degree of isolation in the Flemish Cap. The Flemish Pass hinders the migration to and from surrounding areas like the Grand Banks for juvenile and adult stages of shallow demersal species, such as Atlantic cod Gadus morhua (Templeman and Fleming 1963, Konstantinov 1970) and American plaice Hippoglossoides platessoides (Morgan and Bowering 2004). Meanwhile the anti-cyclonic gyre produces a retention effect on eggs and larvae that would eventually stay over the Flemish Cap and recruit to the population.
2.- Fishing history:
Intense fishing activity in the Flemish Cap started in 1960, but it was in 1977 with the establishment of the Exclusive Economic Zone (EEZ) when fishing pressure on cod Gadus morhua, redfish (Sebastes marinus, but especially S. mentella and S. fasciatus) and American plaice Hippoglossoides platessoides increased remarkably, especially in the late 1980’s and early 1990’s. In addition to the decline of stock biomass, since 1960 the average age of cod catches experienced a marked and sequential reduction, from ages 5-9 in the 1960´s to ages 2-4 in the early 1990’s, parallel to the outstanding decline of the Spawning Stock Biomass (SSB). In 1998 the cod stock was declared collapsed, although it was already exhausted in 1995, like the American plaice and redfish fisheries. This fishing resources where then replaced by two new emerging stocks, Greenland halibut Reinhardtius hippoglossoides and Northern shrimp Pandalus borealis, which hoarded most catches in Flemish Cap fishery since 1992. After years of high productivity, in 2005 Northern shrimp catches started a declining trend and in 2010 in was declared collapsed, while the Greenland halibut fishery was subjected to a recovery plan. Flemish Cap cod fishery was reopened in 2010.
Fishing landings were obtained from the NAFO website http://www.nafo.int/about/frames/about.html.
3.- Changes in the demersal community:
The indexes of biomass from the EU annual July surveys showed that across the period 1988-2008, the most abundant demersal species in the Flemish Cap were cod, redfish, Northern shrimp and Greenland halibut accounting, as an average, for the 83.5% of total index of biomass every year. Analyses of biomass trajectories showed that, as was also evidenced by fishing landings, the demersal community experienced notable variations across the period 1988-2008. The collapse of cod stock in the mid 1990’s was followed by the increase of shrimp and Greenland halibut. The Genus Sebastes showed a sudden increment starting since year 2003, and reached to biomass levels never observed before. Water temperature, fish predation and fishing activity were significant drivers of the Flemish Cap demersal community (Pérez-Rodríguez et al, 2012).
Biomass index from the EU bottom trawl annual surveys conducted on July in the Flemish Cap since 1988. Upper figure: Left axis: Gadus morhua, Reinhardtius hippoglossoides and Pandalus borealis. Right axis: Sebastes spp. Lower figure: biomass index for species of genus Sebastes.
Parallel to these changes in biomass of most important demersal species, feeding habits also experienced marked variations. The dominant trend was the increase of shrimp in the diet of cod, redfish and Greenland halibut since late 1990’s; but also the higher importance of redfish in the diet of cod and Greenland halibut. In parallel, there was a decline of importance in the diet of their usual preys like hyperiids and copepods. Main drivers for these variations in the diet were the abundance of different preys, competition and water temperature (Pérez-Rodríguez et al, 2011).
Feeding habits of cod (upper panel: juvenile <46cm; bottom panel: adult >46cm) across the period 1993-2012.
Recently, variations in total consumption of shrimp by cod and redfish, as well as consumption of redfish by cod, have been found to be negatively related with biomass of both prey species (Pérez-Rodríguez & Saborido-Rey, 2012). Hence, predation has seems to be highly important in the dynamic of Flemish Cap demersal community while changes in biomass of prey were main drivers for diet composition, i.e. a strong interrelationship between population dynamic and feeding habits in the Flemish Cap.
In addition, since late 1970, important variations in cod stock productivity through the variations in growth, condition, maturation and reproductive potential were detected (Pérez-Rodríguez et al 2011, 2013), which were related with high fishing pressure and changes in water temperature.
These results highlight the importance of looking at commercial population dynamic from a comprehensive perspective. Fishing, maturation and reproduction, fish growth, oceanography and trophic interactions have to be considered at once for a more realistic approach to the management of interacting populations. This is the main aim of GADCAP through the development of a GADGET multispecies stock assessment model for the Flemish Cap cod, redfish and shrimp in the bossom of NAFO.
GADCAP 