160
C. Odebrecht and J.P. Castello
cia! species are the Brazilian sardine (Sardinella brasiliensis), skipjack
(Katsuwonus pelamis), Argentine anchovy (Engraulis anchoita), albacore
(Thunnus alalunga), bigeye tuna (T. obesus), swordfish (Xiphias gladius)
and yellowfin tuna ( T. albacares; Fig. 11.3D ). Fisheries of an almost virgin
stock of Argentine anchovy (average 25 x 10 3 tons off the northern coast of
Argentina) and skipjack have potential for expansion. Smaller yields of
traditional bony fish fisheries have increased the fishing pressure on elasmobranchs (bottom and pelagic sharks and rays). Today, elasmobranchs
(mainly Galeorhinus galeus, Mustelus schmitti, Prionace glauca; Vooren
1997) represent about 10% (49-55 x 10 3 tons between 1994 and 1998) of
demersal catches in southern Brazil and 3.2 o/o of the total catch in Argentina (Bonfil 1994). Squid (Illex argentinus, Loligo sp.) are fished in large
quantities (1989 >700 x 10 3 tons, 1995 560 x 10 3 tons) by Argentinean and
foreign fishing boats. Shrimps (Artemesia longinaris, Pleoticus muelleri,
Farfantepenaeus paulensis, F. brasiliensis) are coastal fishery resources
exploited by industrial fisheries in Brazil and Argentina and artisanal
fisheries in Uruguay (Fig. 11.3A).
11.6.2 Pollution and Blooms
Potentially hazardous materials reach the shelf and slope ecosystem
through direct discharge from coastal urban and industrial centers, via
continental freshwater runoff, or as a result of marine accidents. Owing to
natural background levels (Niencheski et al. 1994; Seeliger and Costa
1997), except for copper and lead, metal contribution from the Patos
Lagoon is likely to be negligible, though mercury discharge from the Rio
de la Plata (Kurucz et al. 1998) is of concern. Agrotoxics from extensive
agricultural lands in the Rio de la Plata and Patos Lagoon watershed
will ultimately reach offshore waters and biota. Furthermore, large-scale
agricultural activities and industrial and domestic effluents add excess
nutrient loads, especially nitrogen, which increases phytoplankton production and changes the species composition. Algal blooms are a common
feature off southern Brazil, Uruguay, and Argentina and red-colored surface patches have been registered since the beginning of the century.
Harmful dinoflagellate (Alexandrium tamarense, Gymnodinium catenatum, Dinophysis acuminata) blooms cause paralythic and diarrhetic shellfish poisoning (Mendez et al. 1998). The potentially deleterious effect of
increased UV radiation during the austral spring up to 30°S (Seeliger and
Costa 1997) is likely to modify abundance, productivity, and trophic dynamics of the system. Red tide dinoflagellates of stable, high irradiance environments tend to be more tolerant to UV photoinhibition (Carre to et al.
C. Odebrecht and J.P. Castello
cia! species are the Brazilian sardine (Sardinella brasiliensis), skipjack
(Katsuwonus pelamis), Argentine anchovy (Engraulis anchoita), albacore
(Thunnus alalunga), bigeye tuna (T. obesus), swordfish (Xiphias gladius)
and yellowfin tuna ( T. albacares; Fig. 11.3D ). Fisheries of an almost virgin
stock of Argentine anchovy (average 25 x 10 3 tons off the northern coast of
Argentina) and skipjack have potential for expansion. Smaller yields of
traditional bony fish fisheries have increased the fishing pressure on elasmobranchs (bottom and pelagic sharks and rays). Today, elasmobranchs
(mainly Galeorhinus galeus, Mustelus schmitti, Prionace glauca; Vooren
1997) represent about 10% (49-55 x 10 3 tons between 1994 and 1998) of
demersal catches in southern Brazil and 3.2 o/o of the total catch in Argentina (Bonfil 1994). Squid (Illex argentinus, Loligo sp.) are fished in large
quantities (1989 >700 x 10 3 tons, 1995 560 x 10 3 tons) by Argentinean and
foreign fishing boats. Shrimps (Artemesia longinaris, Pleoticus muelleri,
Farfantepenaeus paulensis, F. brasiliensis) are coastal fishery resources
exploited by industrial fisheries in Brazil and Argentina and artisanal
fisheries in Uruguay (Fig. 11.3A).
11.6.2 Pollution and Blooms
Potentially hazardous materials reach the shelf and slope ecosystem
through direct discharge from coastal urban and industrial centers, via
continental freshwater runoff, or as a result of marine accidents. Owing to
natural background levels (Niencheski et al. 1994; Seeliger and Costa
1997), except for copper and lead, metal contribution from the Patos
Lagoon is likely to be negligible, though mercury discharge from the Rio
de la Plata (Kurucz et al. 1998) is of concern. Agrotoxics from extensive
agricultural lands in the Rio de la Plata and Patos Lagoon watershed
will ultimately reach offshore waters and biota. Furthermore, large-scale
agricultural activities and industrial and domestic effluents add excess
nutrient loads, especially nitrogen, which increases phytoplankton production and changes the species composition. Algal blooms are a common
feature off southern Brazil, Uruguay, and Argentina and red-colored surface patches have been registered since the beginning of the century.
Harmful dinoflagellate (Alexandrium tamarense, Gymnodinium catenatum, Dinophysis acuminata) blooms cause paralythic and diarrhetic shellfish poisoning (Mendez et al. 1998). The potentially deleterious effect of
increased UV radiation during the austral spring up to 30°S (Seeliger and
Costa 1997) is likely to modify abundance, productivity, and trophic dynamics of the system. Red tide dinoflagellates of stable, high irradiance environments tend to be more tolerant to UV photoinhibition (Carre to et al.