Seasonal and Regional Variation in Egg Size of the Argentine Anchoita

517 Abstract—Eggs of the Argentine anchoita (Engraulis anchoita) are very Seasonal and regional variation in egg size of the abundant and frequently collected in research ichthyoplankton tows along Argentine anchoita (Engraulis anchoita) in the the southern–southeastern Brazilian southeastern Brazilian Bight coast. The commercial exploitation of Argentine anchoita has also recently begun in southern Brazil. Therefore, Jana M. del Favero (contact author)1,3 there is a need for a better under- Mario Katsuragawa1 standing of the population structure Fabricio S. C. Oliveira2 and dynamics of this species in or- 1 der to manage the fishery for this Nayara C. Tannure species. Our objective was to deter- M. L. Zani-Teixeira1 mine seasonal and regional variabil- Jefferson T. Turner3 ity in the size of eggs of Argentine anchoita in the southeastern Brazil- Email address for contact author: [email protected] ian Bight (SBB). Because there are no physical barriers in the ocean, 1 defining stock limits for fish popula- Instituto Oceanográfico tions is difficult, particularly for a Universidade de São Paulo semimigratory species such as the Praça do Oceanográfico, 191 Argentine anchoita. Eggs from the 05508-120, São Paulo, SP, Brazil south of the SBB were larger than 2 Instituto de Oceanografia those from the north, indicating that Universidade Federal do Rio Grande eggs from the northern Santa Marta Avenida Itália km 8 Cape region probably belong to the 96203-900, Rio Grande, RS, Brazil bonaerense stock. Also, eggs collected 3 School for Marine Science and Technology during the winter were larger than University of Massachusetts Dartmouth those collected during the summer. 706 S. Rodney French Boulevard This difference in egg size may be New Bedford, Massachusetts 02744-1221 due to either 1) larger adults com- ing from the south and spawning in or closer to the area sampled during winter, or 2) an adaptive response of spawning females to the changes in the abiotic conditions or 3) a combi- Most marine fish eggs are identi- Blaxter and Hempel, 1963; Blaxter nation of these 2 features. fied by their size, shape and pigment and Hunter, 1982; Marteinsdottir characters, but many newly fertilized and Able, 1992). eggs are unpigmented and therefore The Argentine anchoita (Engrau- egg diameter is the most distinguish- lis anchoita) (Engraulidae: Clupe- ing feature (Bagenal, 1971). Auto- iformes) is a small pelagic fish, which mated identification of fish eggs, is important as a secondary consum- based on their size and shape (Fa- er near the bottom of the food chain, vero et al., 2015) is possible; how- and is an essential prey for other ever, egg size varies among species, fish species, marine mammals, and among populations, and within pop- seabirds (Castello, 2007). It is eco- ulations of the same species owing nomically important to the Argentine to temporal, spatial, biological, and and Uruguayan fishery fleets (FAO, Manuscript submitted 27 October 2016. environmental factors (e.g., Phonlor, 2014), and exploitation of Argen- Manuscript accepted 15 August 2017. 1984; Wootton, 1990; Chambers and tine anchoita has recently begun in Fish. Bull. 115:517–531 (2017). Waiwood, 1996; Llanos-Rivera and southern Brazil (Carvalho and Cas- Online publication date: 1 September 2017. Castro, 2004). In addition to identi- tello, 2013). This species is widely doi: 10.7755/FB.115.4.8 fication of fish eggs, it is important distributed over the continental shelf to understand variation in egg sizes of the southwest Atlantic, from Vito- The views and opinions expressed or implied in this article are those of the because larger eggs typically hatch ria, Brazil (20°S) to Gulf San Jorge, author (or authors) and do not necessarily into larger larvae with the possibility Argentina (48°S) (Castello, 2007). reflect the position of the National of conferring a higher survival poten- There are 3 distinct stocks: the pa- Marine Fisheries Service, NOAA. tial on the resulting offspring (e.g., tagonic (48–41°S), the bonaerense 518 Fishery Bulletin 115(4) (41–27°S) and a third, ranging from 27°S and 20°S, et al., 2000; Gaeta and Brandini, 2006; Piola et al., is known as the “Brazilian Southeastern Bight stock” 2008a; Piola et al., 2008b). (Carvalho and Castello, 2013). Different methods have To address the possible role of spatial (regional) been used to identify the 3 stocks: to distinguish the and temporal (seasonal) variation in egg size of Argen- patagonic from the bonaerense, Hansen (1994) used tine anchoita, we used data collected from 2 different growth rates, size–weight relationships and length sets of research cruises: for the regional variation, the at first maturation; Castello and Castello (2003) com- study area comprised most of the SBB, between Cape pared larval growth and length at first feeding from Frio, in the state of Rio de Janeiro, and Cape Santa southeastern and southern Brazil; and Carvalho and Marta Grande, in the state of Santa Catarina (roughly Castello (2013) analyzed size and age composition and between 23°S and 28°S). For the seasonal variation, length-at-age data and concluded that anchovies from the study was carried in the northern part of the SBB, the Santa Marta Region (30–27°S) should be consid- from off Cape São Tomé (22ºS) to São Sebastião Island ered as a part of the bonaerense stock. Although the (24ºS), in the state of São Paulo during the summer parameters used cannot reveal the genetic discreteness and winter of 2001 and 2002 (Fig. 1). of these stocks, they are still powerful tools for stock identification purposes (Begg, 2005). In situ data No study dedicated specifically to variation in egg size of the Argentine anchoita has been conducted in To assess the seasonal variation in egg size of Argen- the southeastern Brazilian Bight (SBB; roughly be- tine anchoita, we took advantage of biotic and abiotic tween 22°S and 28°S). A few studies have focused data obtained from a set of 4 oceanographic cruises off the southern coast of Brazil, and the coasts of carried out during the summer and winter of 2001 and Uruguay and Argentina (Ciechomski, 1973; Phon- 2002. During both seasons of 2001, only one transect lor, 1984), but they cover only the bonaerense stock. was performed in the Cape Frio region, but some sam- Therefore, our objective was to evaluate seasonal and pling stations were sampled twice. Summer of 2002 regional variability in the size of eggs of Argentine an- covered 14 transects and winter of 2002 included 13 choita in the SBB, and to consider factors that may transects (Table 1, Fig. 1). cause such variation. In order to address patterns in the spatial variation in egg size of Argentine anchoita, data were obtained from another set of cruises conducted during the sum- Materials and methods mers over 5 years (1975, 1988, 1990, 1991, and 1993; Table 1) and the SBB was divided into 3 areas: area Study area 1 from Cape São Tomé to São Sebastião Island; area 2 from São Sebastião Island to Paranaguá Bay; and The Brazil Current flows southward along the continen- area 3 from Paranaguá Bay to Cape Santa Marta tal slope of the SBB (Silveira et al., 2000) transporting Grande (Fig. 1). These areas were defined on the fol- warm and saline Tropical Water in the upper mixed lowing bases: 1) Argentine anchoita stock identification layer and cold South Atlantic Central Water (SACW) at as defined by Carvalho and Castello (2013) (area 3); the pycnocline. An additional water mass exists in the 2) oceanographic conditions described by Miranda and neritic zone, the warm Coastal Water, with lower salin- Katsuragawa (1991) and Mahiques et al. (2004) (area ity than the Tropical Water (Castro Filho and Miranda, 1 and area 2); 3) a spawning map obtained by Favero 1998). Except for some coastal areas that are under et al. (2017), so that the divisions would not separate the influence of waters flowing from large embayments, any important spawning area. such as Guanabara Bay in the state of Rio de Janeiro, Temperature and salinity data were obtained from oligotrophic conditions prevail in the study area owing Nansen bottles and reversing thermometers in 1975 to the dominance of Tropical Water in the upper layers, and 1988. In the other 3 years, a conductivity, tem- and oceanic nutrients trapped within the SACW (Lopes perature, and depth (CTD) profiler, an SBE 917plus1 et al, 2006). (Sea-Bird Scientific, Bellevue, WA), was used to collect The intermittent coastal upwelling off Cape Frio this information. is an important process that brings the nutrient-rich As described by Smith and Richardson (1977), a SACW into the euphotic zone (Valentin et al., 1987). bongo net with a 0.61-m diameter mouth opening These SACW intrusions vary seasonally, advancing was used to sample ichthyoplankton. It was equipped toward the coast during spring and summer and re- with paired cylindrical-conical 0.333-mm and 0.505- treating toward the shelf break in the autumn and mm mesh-size nets and with a flowmeter attached winter (Cerda and Castro, 2014). Another physical pro- at the center of the mouth opening of each net in or- cess that fertilizes the euphotic zone occurs during the der to measure the volume of filtered water. The net winter, when subantarctic and the Plata River Plume was towed obliquely from the surface to the maxi- waters are driven northward by southerly winds from the continental shelf of Argentina and Uruguay into 1 Mention of trade names or commercial companies is for iden- most of the inner shelf in the south of Brazil and even tification purposes only and does not imply endorsement by the SBB (Brandini 1990; Stevenson et al., 1998; Piola the National Marine Fisheries Service, NOAA.

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