by
E. MORSAN, R. GONZALEZ and M. KROECK
Instituto de Biologia Marina y Pesquera "Almirante Storni", C.C. 104, 8520 - San Antonio O., Argentina (e-mail: biolmar@canaldig.com.ar)
Summary
The shortfin squid, Illex argentinus,is caught as by catch of hake (Merluccius hubbsi)by the trawler fleet in the San Matías Gulf (SMG) demersal fishery. Size distribution, gonadal stages and parasitic composition were recorded monthly for three years: 1991 - 1993. Two demographic units were identified from the sample analysis: Spring Spawning Stock (SPR) and Summer Spawning Stock (SSS). Since 1994, 5 jiggers were admitted to fish from June to August each year. Spatial and temporal variation of CPUE annual series were analyzed. Demographic, parasitic composition and fishery information supports the hypothesis of immigration from the continental shelf to SMG during late fall - winter. Recruitment inside SMG may fail due to spring low sea water temperatures.
15-25 cm) in maturing condition was recorded.
Both stocks, composed by adults individuals, co-exist in late spring, and evidences of coupling (spermatophores in the gill) were observed in mature females.
The above mentioned stocks agree with Spring Spawning Stock (SPR) and Summer Spawning Stock (SSS) described by Brunetti y Pérez Comas (1989).
Seven parasite taxa were identified in the samples: 3 cestodes and 4 nematodes. Prevalence and mean intensity of the three main parasitic entities (Scolex polymorphus, S. pleuronectisand Anisakis sp) had a gradual increment with squid age. The enteric parasitic fauna found in SPR and SSS are similar in species composition, but prevalence and mean intensity were higher in SPR than SSS.
The role of main parasites in other subpopulations inhabiting neighboring areas of the Argentine Shelf waters are occupied by cestodes larvae as Phillobothrium sp, Dinobothriumsp and Pelichnibothriumsp. These differences in parasitic species composition may be caused by biotopic isolation of SPR and SSS stocks in the San Matias Gulf, in a important part of its life cycle (González & Kroeck, 1994).
Jigging fishing began in 1994. In August, five jiggers were licensed to fish experimentally in SMG. Catch reached 715 ton after 21 fishing days, and was entirely composed by SPR individuals.
Catch in subsequent fishing seasons were widely variable: 1995 = 914 tons , 1996 = 136 tons; 1997 = 1742 tons. CPUE values have shown high spatial-temporal contrast between years (Fig 1). The analysis of fleet spatial distribution shows a clear pattern: each year, the degree of clumping is correlated with stock availability. When daily catches were high, vessels didn't change its position and remained in same site until CPUE decreased at an acceptance limit. If low daily catches have taken place, the fleet tends to explore a greater area and to scatter effort allocation (e.g.: 1996).
Fig. 1. Times series of mean daily CPUE (kg/h.line) Four seasons (1994 - 1997)). In maps:
spatial effort allocation and individual CPUE (Circle diameters)
This fishing behavior of jigging fleet (a diurnal exploration phase and nocturnal fishing phase) produced an oscillating trend in CPUE time series, as a response to local depletion of squid concentrations.
In 1995 and 1996, maximum CPUE was reached at the beginning of fishing season, followed by a slow declining trend. In remaining years, an increasing slope may represents an accumulative effects of immigration and stock concentration. The Leslie - DeLury methods were applied only in 1996 and 1997, resulting in 197 tons and 3161 tons, respectively. Critical difficulties were found to apply linear regression due to the nature of data. Changes in stock concentration and sequential harvesting could produce changes in catchability, so that, CPUE is not proportional to abundance. If an immigration rate of short-lived squid takes place during the fishing season, estimate is possible only when
Seminario Final Proyecto INIDEP - JICA, 1999 163 stock is fully available, after immigration and
before declining by natural mortality (Caddy, 1991).
The absence of ommastrephid larvae in plankton surveys and juvenile squids in the samples, the seasonal features of squid landing by trawl fleet and changes in catch rates of jigging fleet, supports the hypothesis of squid stocks immigration from the Continental Shelf to SMG during winter. In spite of spawning takes place inside SMG (80 % mature female with spermatophores in SPR), recruitment may fail due to sea water low temperatures in spring. The SPR would migrate to SMG during late fall - early winter period, changing its diet composition, and segregating itself from other stocks. Gradually, the development of reproductive aggregations modify the spatial pattern of stock distribution, conditioning the fleet movements and catch rates.
References
Brunetti, N. E., Pérez Comas. 1989. Abundancia distribución y composición poblacional del
recurso calamar (Illex argentinus) en aguas de la plataforma patagónica en diciembre de 1986 y en marzo y mayo de 1987. Frente Maritimo 5ª: 39-59.
Caddy, J. F. 1991. Daily rings on squid statoliths:
an opportunity to test standar population models? In P. Jereb, S. Ragonese & S. von Boletzky (eds) Squid age determination using statoliths. NTR - ITPP Sp Publ N1.
González, R. A. & Kroeck, Enteric helminths of shortfin squid Illex argentinus(Castellanos,
1960) in San Matias Gulf. MS
Morsan, E. M. & R. A. González. 1996. Sobre la presencia de dos unidades demográficas de la población de calamar (Illex argentinus) en el Golfo San Matías. Frente Marítimo 16(A): 125-130.
Nigmatulin, CH. M 1989. Las especies más abundantes de calamar del Atlántico sudoeste y sinopsis sobre la ecología del calamar (Illex argentinus). Frente Marítimo 5(A): 71 - 81.
Pierce, G. 1994. Stock assessment methods used for cephalopods fisheries. Fish Res 21(1-2):
255 - 286.
Seminario Final Proyecto INIDEP - JICA, 1999 165
Introduction
Bottom trawling off southern Brazil has developed during the 1960´s and has traditionally targeted few groundfish species and penaeid shrimps. This fishery has always produced an abundant and diverse by-catch that includes high-priced shellfish species which, due to the decline of commercial stocks, have become progressively valued motivating emerging directed fisheries (Perez and Pezzuto 1998).
Abundantly caught by the trawling fishery off Santa Catarina state, southern Brazil, the squid Loligo plei, has sustained large but oscilating catches that peaked in 800 t in 1986. Artisanal inshore catches have also been reported never surpassing 10% of total squid catch (IBAMA, 1994). This paper describes the squid fishery structure in Santa Catarina and analyses its dynamic patterns.
Materials and methods
The squid fishery has been studied from (a) reported landings registered by the Brazilian Institute for the Environment (IBAMA) from 1989 to 1997, and (b) from a fishery sampling program conducted in the Itajaí harbor (offshore fishery) and in coastal fishing communities (inshore fishery) since 1995 (Perez et al. 1998;
Perez et al. 1999). The latter source provided, through interviews with skippers at the moment of the landings, information on fishing methods, seasons and areas as well as catch and effort.
Fishing trips were considered measures of effort for the IBAMA catch series. An effort standardization procedure was conducted by estimating each vessel´s catch per trip (CPUE) and its fishing power (Sparre and Venema, 1992).
The analysis included December to March landings and required a selection of fishing trips Summary
The squid Loligo plei, has been an important component of the trawl fishery by-catch in Santa Catarina State, southern Brazil., and has originated, in recent years, directed inshore and offshore fisheries. The structure and dynamics of this fishery have been studied since 1995 from Brazilian government landing statistics and from a fishery sampling program developed in the Itajaí harbor and coastal fishing communities. Both offshore and inshore catches concentrate in the summer months. Offshore fisheries is conducted by double rig trawlers and pair trawlers on the northern shelf between the 20 and 45 m isobaths.
The inshore fisheries is conducted in coastal waters, both by fish traps and directed hand jigging. Catches are sustained by an annual cohort that becomes available in December and disappears in March-April, reaching a biomass within this period. Incidental landings of shrimp trawlers in December stimulate fish and pair trawlers to join the fishery later in the season. In recent years all vessels involved have become more specialized, adjusting their catches to biomass peaks.