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Utilization patterns of surfzone inhabiting fish.

35

A complementary pattern of size distribution was observed through the monthly gonadal maturation stages of H. clupeola. Individuals of initial maturity stage (B) began to appear in the surf zone in November and continued until January, when first maturity (C) fish occurred and initial maturity stage individuals increased to 70%. Subsequently, only immature individuals were caught, a similar pattern to those observed on the initial months (June to October) (Fig. 5).

Lenanton 1984, Lasiak 1986, Reina-Hervas & Serrano 1987, Clark 1997), and thus, this environment has been recognized as nursery by many studies (Gunter 1938, Gibson 1973, Ruple 1984, Ross et al. 1987, Bennet 1989, Whitfield 1989, Godefroid 1996). The beaches studied in the present investigation are considered accessory nursery areas, since they are near the Paranaguá estuarine complex and are used by most species during at least part of their life cycle.

Figure 5. Harengula clupeola. Occurrence of gonadal maturation stages occurrence between Jun/04 and May/05 for in

surf zone habitats in Pontal do Paraná, Brazil. (

immature

individuals - A,

individuals in maturation - B and

mature individuals - C).

In general, most species are characterized as seasonal or sporadic migrants, with few species considered as truly resident (McLachlan 1983). According to Day (1951), estuarine resident species are those that spend their entire life cycle within the estuary. This definition of resident species can be applied to species that are represented by all maturity stages and are constant throughout the year in beach environments. Modde (1980) appointed T. carolinus, scaled herring Harengula jaguana Poey 1865, M. littoralis and other three species as residents on Gulf of Mexico beaches. However, in the present study, none could be considered as resident, because no species were captured in all gonadal maturation stages according to Vazzoler (1981) macroscopic scale.

Discussion

An inherent characteristic of sand beach ichthyofauna is the dominance of the assemblages by a few species (McFarland 1963, Modde & Ross 1981). Such a pattern could be viewed from the evolutionary perspective of the occupation of this environment, where only a few species succeeded to reproduce and to remain in a turbulent and mutable habitat. Great quantities of clupeiforms inhabiting surf zones were found by several authors (McFarland 1963, Beckley 1984, Lopes et al. 1993), indicating the massive utilization of this habitat by a typical transient fauna between estuarine and open sea environments (Strydom 2003).

In addition to clupeids and engraulids, carangids and sciaenids, such as T. carolinus and M. littoralis respectively, are common in the surf zone, and are widely documented along beaches around the world (Ross 1983, Modde & Ross 1983, Nelson 1986, Ross & Lancaster 2002). These species are zooplanktophagous and their juveniles find abundant food supply, protection against predators and shelter in low visibility shallow water habitats of oceanic and estuarine beaches (Clark et al. 1994, Nash & Santos 1998).

Despite net selectivity, juvenile is the most frequently found stage in sand beaches (Robertson &

Recruitment patterns are the result of seasonal changes in abundance and diversity on surf zone fish, which could be determined by reproductive activity and coastal circulation (Ross et al. 1987) or either by emigration or exploration of high productive areas by adults (Allen 1982). High diversity and abundance are found in warmer months while colder months show low values (Fox & Mack 1968, Naughton & Saloman 1978, Modde & Ross 1981, Ross 1983, Lasiak 1984). In addition, Godefroid (1996) and Monteiro-Neto et al. (1990) found the lowest numbers of fish during spring at Southern Brazil beaches, which are results similar to those observed in the present study. The peak value of evenness occurred during September, when equal species contribution was related to low number of species and individuals, as shown by Nash & Santos (1998). On the other hand, large aggregates of O. bonariensis and H. clupeola occurred in June and July, which consequently

decreased the evenness index.

Taking

into

consideration

several

investigations conducted near the studied area (Godefroid 1996, Rocha et al. 2002, Godefroid et al. 2004, Spach et al. 2004), we suggest that most fish concentrate their reproductive effort over spring and summer. During this period, high temperatures favour phytoplankton production and consequently,

Pan-American Journal of Aquatic Sciences (2007), 2 (1): 27-39

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