Age estimation of brown shrimp Crangon crangon: comparison of two approaches applied to populations at the biogeographic edges

Abstract

In this study, 2 methods for age estimation of Crangon crangon were compared: one based on total length, the other based on the number of segments in the antennules, as suggested by Tiews' findings (1954: Ber Deut Wiss Kommiss 13:235−269). Shrimps from populations near the species' geographic edges, from Valosen Estuary (Norway) in the north and the Minho Estuary (Portugal) in the south, were used. These showed great individual variability in shrimp size growth and in antennule segment number increment, due to the presence of fast-and slow-growing shrimps in the 2 populations, implying that shrimps of different ages may have similar sizes, as well as similar segment numbers. Additionally, the origin of shrimp population, sex, length and segment number, and water temperature were found to influence growth, both in the length-and the segment-increment models, often being interacting parameters. Both methods resulted in growth curves similar to a typical von Bertalanffy growth curve. The growth rate was higher for females than for males and positively related to temperature; the maximum size was also larger for females. In contrast, maximum segment number was larger for males than for females, as has also been found by Tiews (1954). The 2 models resulted in considerably different age estimates, particularly for older shrimps (i.e. shrimps of larger size or with more antennule segments). The models also suggest site-specific growth rates. Any age estimation approach will therefore need to be validated for each population. KEY WORDS: Crangon crangon · Age estimation · Growth · Moult · Temperature · LatitudeResale or republication not permitted without written consent of the publisher Aquat Biol 19: 167-184, 2013 requires optimum conditions, which under natural environments are seldom observed.Results from these works cannot be generalized for the entire geographic range of the species, given the latitudinal compensation which has recently been described for the growth rate under controlled food and temperature conditions (Campos et al. 2009). Instead of a reduced growth rate of northern shrimps following the latitudinal thermal gradient, as would be expected (i.e. assuming that the lower temperature regime at higher latitudes slows down growth), a 'latitudinal compensation' was observed, whereby northern shrimps grew faster than shrimps from a southern population kept at the same temperature regime. In contrast, a recent field-based study near the southern limit of the species' distribution speculates that southern shrimps grow more slowly, mature earlier and have smaller brood sizes, and that their larvae have a more protracted settlement period than northern populations (Viegas et al. 2012). However, the comparison was made between non-contemporaneous studies, which limits conclusions, since inter-annual fluctuations in both shrimp abundance (Campos et al. 2010) and timing of biological stages are frequent (e.g. Oh et al. 1999).Growth studies on crustaceans are further problematical because no hard str...

Reproduction and recruitment of the brown shrimp Crangon crangon in the inner German Bight (North Sea): An interannual study and critical reappraisal

“…Minimum numbers (<10%) of ovigerous females within the annual cycle were present between August and early December (Siegel et al, ). Fast growth, the extended reproductive period and the lack of accurate age determination methods (Campos, Bio, Freitas, Moreira, & van der Veer, ) render cohort analysis and, thus, age‐based assessments of C. crangon stocks almost impossible. Consequently, fisheries targeting brown shrimp have been difficult to manage and to regulate.…”