35
fisheries targeting benthic resources such as scallops also show clear relations to fronts.
Stocks of Patagonian scallop (Zygochlamys patagonica) are widely distributed over the
western South Atlantic shelf but exploitation is carried out on large, discontinuous, recurrently located concentrations that match front locations (Bogazzi et al. 2005). In the western North Atlantic, the highest concentration of many permanent beds of the Sea Scallops
(Placopecten magellanicus) appears to correspond to areas where physical oceanographic
features such as fronts and gyres may keep larval stages in the vicinity of the spawning
population (Hart and Chute 2004).
4.2 Conservation Issues
High biological productivity at fronts concentrates several kinds of species,
improving their foraging opportunities; consequently, interactions between fisheries and vulnerable or endangered species are amplified at fronts. Large marine
vertebrates, such as sea turtles, marine mammals and seabirds, have little or no
commercial value, but become hit, entangled or hooked accidentally by fishing gears that are intended for valuable target species (Lewison et al. 2004). Blue
sharks are commonly caught as bycatch in longlines targeting swordfish and
tuna species in the northeast Atlantic (Queiroz et al. 2012). In the North Atlantic,
leatherback turtle (Dermochelys coriacea) forage along productive fronts where
their main prey, gelatinous plankton, is concentrated. This is also where pelagic,
longline fishing boats aggregate and take a number of sea turtles as bycatch
(Ferraroli et al. 2004). Loggerhead sea turtles (Caretta caretta) travel across the
Pacific between their nesting beaches in Japan and Australia and their foraging
habitat in the eastern Pacific. Juvenile sea turtles travel westward, against prevailing currents, along two convergent thermal fronts. This behavior appears to
explain the highest incidental catch rates of loggerheads in the Hawaiian longline
fishery (Polovina et al. 2000). Around the Azores islands in the Atlantic Ocean,
Caretta caretta juveniles are incidentally caught in drifting longlines that target
swordfish, Xiphias gladius. High catch rates coincide with the presence of thermal
fronts and eddies, which are related to major currents and bathymetric characteristics (Ferreira et al. 2011).
Marine birds exploit preys concentrated at ocean fronts, where fisheries discards seem to provide a good food source. Around the Brazil-Malvinas Confluence
(a major frontal region in the Southwestern Atlantic), the high concentration
of bird’s preys and the aggregation of fisheries resources (swordfish, tunas and
pelagic sharks) lead to the overlap of industrial fisheries with albatross and petrels. This region has one of the highest levels of incidental capture of albatross and
petrels across global longline fisheries (Jiménez et al. 2011). Along the Patagonian
shelf break front, albatrosses (e.g. wandering albatrosses Diomedea exulans) foraging areas overlap with longline fisheries directed to the Patagonian toothfish
(Dissostichus eleginoides) which could lead to increased incidental mortality of
these vulnerable bird species (Xavier et al. 2004).
4.1 Fisheries
fisheries targeting benthic resources such as scallops also show clear relations to fronts.
Stocks of Patagonian scallop (Zygochlamys patagonica) are widely distributed over the
western South Atlantic shelf but exploitation is carried out on large, discontinuous, recurrently located concentrations that match front locations (Bogazzi et al. 2005). In the western North Atlantic, the highest concentration of many permanent beds of the Sea Scallops
(Placopecten magellanicus) appears to correspond to areas where physical oceanographic
features such as fronts and gyres may keep larval stages in the vicinity of the spawning
population (Hart and Chute 2004).
4.2 Conservation Issues
High biological productivity at fronts concentrates several kinds of species,
improving their foraging opportunities; consequently, interactions between fisheries and vulnerable or endangered species are amplified at fronts. Large marine
vertebrates, such as sea turtles, marine mammals and seabirds, have little or no
commercial value, but become hit, entangled or hooked accidentally by fishing gears that are intended for valuable target species (Lewison et al. 2004). Blue
sharks are commonly caught as bycatch in longlines targeting swordfish and
tuna species in the northeast Atlantic (Queiroz et al. 2012). In the North Atlantic,
leatherback turtle (Dermochelys coriacea) forage along productive fronts where
their main prey, gelatinous plankton, is concentrated. This is also where pelagic,
longline fishing boats aggregate and take a number of sea turtles as bycatch
(Ferraroli et al. 2004). Loggerhead sea turtles (Caretta caretta) travel across the
Pacific between their nesting beaches in Japan and Australia and their foraging
habitat in the eastern Pacific. Juvenile sea turtles travel westward, against prevailing currents, along two convergent thermal fronts. This behavior appears to
explain the highest incidental catch rates of loggerheads in the Hawaiian longline
fishery (Polovina et al. 2000). Around the Azores islands in the Atlantic Ocean,
Caretta caretta juveniles are incidentally caught in drifting longlines that target
swordfish, Xiphias gladius. High catch rates coincide with the presence of thermal
fronts and eddies, which are related to major currents and bathymetric characteristics (Ferreira et al. 2011).
Marine birds exploit preys concentrated at ocean fronts, where fisheries discards seem to provide a good food source. Around the Brazil-Malvinas Confluence
(a major frontal region in the Southwestern Atlantic), the high concentration
of bird’s preys and the aggregation of fisheries resources (swordfish, tunas and
pelagic sharks) lead to the overlap of industrial fisheries with albatross and petrels. This region has one of the highest levels of incidental capture of albatross and
petrels across global longline fisheries (Jiménez et al. 2011). Along the Patagonian
shelf break front, albatrosses (e.g. wandering albatrosses Diomedea exulans) foraging areas overlap with longline fisheries directed to the Patagonian toothfish
(Dissostichus eleginoides) which could lead to increased incidental mortality of
these vulnerable bird species (Xavier et al. 2004).
4.1 Fisheries