Seasonal and Spatial Changes of Cephalopods Caught in the Cabo Frio (Brazil) Upwelling Ecosystem

BULLETIN OF MARINE SCIENCE, 52(2): 751-759, 1993 SEASONAL AND SPATIAL CHANGES OF CEPHALOPODS CAUGHT IN THE CABO FRIO (BRAZIL) UPWELLING ECOSYSTEM Paulo Alberto S Costa and Flavio da Costa Fernandes ABSTRACT Variations in the distribution and abundance of coastal cephalopods in the Cabo Frio (Brazil) region were studied from 71 trawl samples obtained between November 1986 and October 1988. Species abundance was compared over the depths sampled and their relationship with hydrological features investigated. Best catches were markedly associated with upwelling of nutrient-rich water (South Atlantic Central Water) during the spring-summer period, at depths from 45 to 60 m. Two species, Lo/igo sanpaulensis and Eledone massyae, account for most of this increase. Variations in abundance of these species are related to recruitment and periods of high productivity on the feeding grounds. Benthic octopods such as Octopus tehuelchus, O. vulgaris and Eledone gaucha occurred in small numbers at 60 m. Species broadly distributed in the western Atlantic, such as Semirossia tenera and Lo/igo plei, were also present. Along the Rio de Janeiro coast (central-southern Brazilian littoral), peak squid catches in demersal fisheries occur from November to April (mid spring to early autumn), when northeastern and eastern winds create coastal upwelling off the Cabo Frio region (Costa and Haimovici, 1990). During this period, prevailing E-NE winds drive the Brazil Current surface waters offshore by Ekman transport, allowing the deeper and cooler South Atlantic Central Water to surface along the coast (Ikeda et aL, 1971; Mascarenhas et aL, 1971; Magliocca et aL, 1979). In summer, however, local phytoplankton blooms of less than 1 day, and low intensity (max. 6 /lg·liter-I of chlorophyll a) occur (Valentin, 1984; Valentin et aL, 1985). Although not comparable to the great upwelling regions (west Pacific and Atlantic coasts), the Cabo Frio upwelling area constitutes a peculiar ecosystem of the tropical Brazilian coast. The water masses of tropical oceans are the basic environmental matrix within which fisheries ecosystems must be studied (Longhurst and Pauly, 1987). The characteristics of a coastal upwelling system that determine its biological and fisheries impacts are rather complex. Here one frequently encounters concentra- tions of seabirds, pelagic fishes and other evidence of enhanced biological production. Voss (1983) and Rathjen and Voss (1987) discussed the aspects of cephalopod migrations and cited temperature as the prime factor. They suggested a probable relationship between seasonal temperatures, prevailing winds, and the inshore arrival of long-finned squid in southern New England in spring. A strong El Nino condition in the equatorial Pacific during 1983 elevated the sea water temperature along the California coast resulting in a reduction in squid production of 60 to 80% compared with the average catch. The purpose of this study is to examine the relationship between the presence of cephalopods in a tropical upwelling ecosystem and the environmental data to understand the fishery variations. MATERIAL AND METHODS Cephalopods were sampled monthly at depths of 30, 45 and 60 m with 20-min day-time hauls in the Cabo Frio region, central southern Brazilian littoral (23"S; 42°W), between November 1986 and 751 752 BULLETINOFMARINESCIENCE.VOL.52. NO.2. 1993 ~ ,,11'" -~. ~ ,, ,, ,I I .RW DE JANEIRO ,I I ,, , <'" \ .i'" .•••------ '/ ,, ' -------"" '--100- ./ ATLANTIC OCEAN Figure I. Map of the Cabo Frio region showing where the trawls were taken. Oceanographic stations 1-6 were at depths of 30, 45 and 60 m. October 1988. The hauls were taken aboard the Research Vessel SUBOFICIALOLIVEIRA(Brazilian Navy). using an otter-trawl with 12 m footrope and cod-end mesh size of 25 mm, towed at approx- imately 3.0 knots. All the hauls were taken from the same area (Fig. I). Samples of near-bottom water were taken with Nansen bottles equipped with reversing thermometers at six stations, at the beginning and at the end of the hauls. Dissolved oxygen was analyzed according to Winkler's method (Strickland and Parsons, 1972) and salinity measured with a Beckman induction salinometer. The dorsal mantle length (ML) of all specimens was measured to the nearest 0.5 mm. The specimens were weighed, their sex determined, and the stage of maturity determined according to the five-step scale outlined by Juanico (J 983) for the squids and a three-step scale outlined by Sanchez (J 976) for the octopuses. All fwld collections were fixed in 10% formalin solution for a 48-h period and preserved in 70% ethanol. Abundance was calculated for each depth; frequencies of each species in the catches are given as the number of tows in which each species was found. The seasonal pattern of abundance was expressed as total biomass (kg·h-I) and its distribution according to the depth was calculated monthly. The mantle length distribution and the species density relationship with temperature range and water masses are also presented. COSTA AND FERNANDES: CEPHALOPODS FROM BRAZIL 753 NW W z o SW f0- e,.) S UJ II:: o SE o E Z ~ NE N NDJ FMAMJ A SON 0 M J A S 0 1986 , 1987 1988 MONTHS Figure 2. Contour plot of the monthly averaged values of surface wind at Cabo Frio region between November 1986 and October 1988. No records from January to April 1988. Contour intervals are 1.5 m·sec·'. RESULTS Hydrography. - The oceanography of Cabo Frio region has been studied since 1968. Available data include local wind stress and hydrographic observations. These records vary in length and completeness, and only temperature and wind intensity were used, and are the most useful for the purpose of this study. Variation in wind direction and intensity (m· secl) causes hydrographic changes through upwelling and changes in the Brazil Current position. Upwelling is favored during the spring-summer period (September to March) when prevailing E-NE winds can attain 9.5 m· sec· I (Fig. 2). The upwelling cycle is interrupted during fall-winter (April to August), when S-SW winds become progressively stronger increasing from 2.5 m 'sec! in Novemberto 7.5 m ·sec·l in June. Monthly variation of temperature, salinity and dissolved oxygen at the three different depths throughout the study period are shown in Figure 3. Bottom temperatures ranged from 13.3° to 24.2°C. The upwelling periods are characterized by the dominance of South Atlantic Central Water (rC < 18°; So/oo < 36.0), mainly during the austral summer, from September to April. Temper- atures were rarely higher than 18°C, and frequently lower than 16°C. Nevertheless, sporadically upwelled waters can also occur throughout the year, according to changes in wind direction and intensity. Colder waters « 14°C)recorded in March and August were caused by atypical E-NE wind and warmer waters (> 21°C) were observed mainly in June, indicating the presence of oceanic water of the Brazil Current (TOC > 18°; So/oo> 36.0), sometimes mixed with coastal water. Bottom salinities ranged from 34.7 to 36.50/00indicating the little variability in the area. Oxygen values varied from 3.54 to 6.62 mi, liter-I. Neither parameter showed a well-defined seasonal pattern. Species Composition and Size Structure. - A total of 2,147 cephalopods, belonging to eight species and four families was recorded, Table 1 lists the total number of individuals caught, their frequencies and the catch rates at each depth. Neritic squids, Loligo sanpaulensis and Loligo plei, amounted respectively to 74.2% and 13.2% of the total catch. Benthic species, Semirossia tenera (6.9%) and Eledone massyae (5.3%), were well represented, while Octopus vulgaris, O. tehuelchus and E. gaucha occurred in small numbers. Two immature specimens of the epipelagic octopod Argonauta nodosa were recorded at 60 m. The mean mantle length increased with depth for most of the species, except 24 ,.'I' .. (.) ' , 0 1\ ' , 22 : '\ ,I '. I i:\ : \ I ! \, I&l , I \ , I a:: ,,. , i I, 20 , I :J , I , : I, ... (/\\ I ,: : / \ ~ , j ~. , \, a:: 18 , , \'d f \ I&l : ; \~i '. C1. \, , /!\ ~ , )/I \/ 16 .I' ." I&l I I ,/ .' ... , ,; ~_•.....~ 14 12 37 36.5 • " 0 ; \'. ~ i"""'0' 0 36 ...>- Z -I ~ rn 35 34.5 34 7 F M A M J J A SON 0 J FMAMJJASO 1987 I 1988 1 months ___ 30m _60m Figure 3. Monthly variation of temperature, salinity and dissolved oxygen. COSTA AND FERNANDES: CEPHALOPODS FROM BRAZIL 755 Table I. Total number of cephalopods caught by depth. Brackets indicate the frequency of capture in the trawls Depths (m) Species 30 45 60 Total % Semirossia tenera 5 (3) 74 (8) 70 (13) 149 (24) 6.9 Loligo sanpalilensis 386 (15) 929 (21) 279 (21) 1,594 (57) 74.2 Loligo plei 57 (8) 177 (11) 46 (7) 280 (26) 13.2 Eledone massyae 8 (3) 106 (14) 114 (17) 5.3 Eledone gaucha 3 (3) 3 (3) 0.13 Octopus vulgaris 4 (4) 4 (4) 0.18 Octopus tehue/chus I (I) I (1) 0.05 Argonauta nodosa 2 (2) 2 (2) 0.09 Number of trawls 24 24 23 71 Total of specimens 448 1,188 511 2,147 Specimens' haul-I 18.7 49.5 22.2 30.3 Diversity (H') 0.64 0.98 1.80 for L. plei, in which it varied without a clear pattern (Fig. 4). The sex ratio was nearly 1:1 for L. sanpaulensis and L. plei. A larger proportion of females was observed for E. massyae and S. tenera. The total number of species increased with depth: three species were found at 30 m, four at 45 m and eight species at 60 m depth. Specific diversity (Shannon's index) also increased with depth; 0.6, 0.9 and 1.8 respectively (Table 1).

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