Potential use of anal fin spines for assessing age and growth of longbill spearfish, <I>Tetrapturus pfluegeri,</I> in the western Atlantic Ocean

Abstract

For the first time, the age and growth of the longbill spearfish, Tetrapturus pfluegeri Robins and De Sylva, 1963, was estimated using transverse sections from the third spine of the anal fin. The samples used were collected in a large zone of the western Atlantic Ocean between 22°N and 36°S, from the artisanal gillnet and commercial longline fleets of Venezuela and commercial longline fleets of Brazil and Uruguay. Von Bertalanffy growth models were fitted by sex and regions, north and south of 7°N. Annual periodicity in ring formation was observed using a marginal increment ratio analysis. The maximum age observed was 7 yrs for females and 6 yrs for males. Differences in growth were found between sexes in the southern, but not in the northern region. In the southern region, female growth was slower and they attained larger sizes (K = 0.42 cm yr–1, L∞ = 184 cm) than males (K = 0.54 cm yr–1, L∞ = 173 cm). In the northern region, longbill spearfish growth appeared faster than in the southern region (K = 0.80 cm yr–1, L∞ = 177 cm). Although more sampling and research is needed, our study provides a starting point for parameter estimation and age validation required for stock assessment of the longbill spearfish in the Atlantic Ocean.