Abstract
Data from 10 acoustic surveys targeting sardine (spring and autumn), 3 acoustic surveys targeting blue whiting (spring) and 9 groundfish surveys (summer and autumn) were used to describe the distribution and relative abundance of snipefish ( Macroramphosus spp.) off Portugal and the Gulf of Cadiz in recent years (1998-2003). Snipefish (8-17 cm) were regularly found off Portugal, occasionally in large concentrations, but were absent from the Gulf of Cadiz. Off northern Portugal, snipefish were distributed along the outer shelf and upper slope, clearly separated from sardine (the most abundant species in the inner shelf) and partially overlapping with blue whiting ( Micromesistius poutassou ), the most abundant species in the upper slope. Snipefish were most abundant in the outer shelf of south-western Portugal, preferentially distributed in large aggregations around the Canyon of Setubal and partially overlapping with the distribution of boarfish ( Capros aper ) and blue whiting (both abundant in the upper slope of south-western Portugal). Off southern Portugal snipefish were almost exclusively distributed in the outer shelf and were significantly smaller than in south-western (intermediate) and northern Portugal (large). Acoustic estimates of total snipefish biomass ranged between 176 – 504 thousand tonnes within the study period, with more than half off south-western Portugal. Within the period 1998-2003, and despite the lack of directed fishing activity, a marked decline in abundance and a small but significant increase in mean length were observed, particularly off south-western Portugal.
Highlights
TABLE 2. – Summary information of the Portuguese acoustic surveys targeting blue whiting used for estimating snipefish distribution and abundance off northern Portugal: survey period, latitude range, acoustic energy attributed to snipefish (Es), number of miles in the survey (Nt), miles with snipefish (Ns), total number of fishing stations (Ht) and number of stations with snipefish (Hs)
The depth distribution of snipefish and acoustically similar species from the groundfish surveys were described by the Generalized Additive
A binomial error distribution with a logit link function was applied to the presence/absence data of all surveys within the study period
Summary
Snipefish of the cosmopolitan genusMacroramphosus occur within the continental shelf (Oliver and Fernandez, 1974; Brêthes, 1979; Clarke, 1984; Silva, 1999), upper slope (Oliver and Fernandez, 1974; Silva, 1999), and oceanic seamounts (Ehrich, 1976; Fock et al, 2002), of all oceans (Fage, 1918). Morais, 1981), suggest that distribution extends as far north as southern Norway and western Scotland in the north-eastern Atlantic > 55o N), snipefish are mainly found between 20 and 40o of latitude in the warm temperate waters of both hemispheres (Brêthes, 1979; Clarke, 1984). Despite the cosmopolitan distribution and the large abundance that snipefish can occasionally attain (Brêthes, 1979; Morais, 1981), relatively little is known on the biology of the species. Reproduction mainly takes place in winter (January-March) in the north-eastern Atlantic (Brêthes, 1979; Morais, 1981; Arruda, 1988; Lopes and Farinha, 1996), and the western Mediterranean (Matallanas, 1982)
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