Seasonality only works in certain parts of the year: the reconstruction of fishing seasons through otolith analysis

Abstract

Seasonality estimations using incremental data usually suffer from small sample sizes and from the lack of comparison with sufficiently large modern samples. The present contribution reports on incremental studies carried out on large assemblages of plaice (Pleuronectes platessa) and haddock (Melanogrammus aeglefinus) from a late medieval fishing village (Raversijde, Belgium) on the North Sea coast. In an attempt to refine previous seasonality estimates made for this site, and to expand conclusions concerning general methodology, extensive monthly samples of modern otoliths of these species, caught within the North Sea, have also been investigated. The modern material shows that the timing of the seasonal changes in the edge type (hyaline or opaque) of the otoliths is extremely variable and that it is dependent on the fishing ground, the year considered, and the age of the fish. It also appears that the increase of the marginal increment thickness is highly variable, to such an extent that the thickness of the last increment of a single otolith is mostly useless for seasonality estimation. Where large archaeological otolith assemblages can be studied, preferably from single depositional events, seasonality determination becomes possible on the condition, however, that the archaeological assemblage corresponds to fish that were captured during their period of fast growth. The growth ring study on the otoliths from Raversijde shows that plaice fishing took place in spring and that it was preceded by a haddock fishing season, probably in late winter/early spring.

Seasonality of human site occupation based on stable oxygen isotope ratios of cod otoliths

“…teeth, bones and fish otoliths has been the principle tool for the interpretation of seasonality in archaeology. Most methods, such as interpretation of tooth replacement and wear and reading of incremental zones in mammal teeth and fish vertebrae and otoliths, rely on validation by comparisons with modern control samples as well as large subfossil vertebrate samples (Van Neer et al, 2004).…”

Pacific cod (Gadus macrocephalus) as a paleothermometer: otolith oxygen isotope reconstruction

“…This growth can be seen in cross section as alternating translucent and dark bands: in Pacific cod, these represent periods of fast growth in the summer and slower growth in the winter. These bands are commonly used to age fish, and they have been used to determine the season of capture, though this remains controversial in an archaeological context Van Neer et al, 2004;West et al, 2011).…”

Validation of otolith δ18O values as effective natural tags for shelf-scale geolocation of migrating fish

“…Seasonality of opaque-translucent otolith banding fluctuates with fish age and latitude in North Sea plaice (Van Neer et al 2004), implying the potential for geographic and individual variation in otolith growth during the year. However, the opaque zone is largely accreted during April to September, and the hyaline (or translucent) zone from October to March (Van Neer et al 2004, authors' pers.…”

“…However, female plaice feed intensely during spring to build reserves for gametogenesis commencing in July (Rijnsdorp 1989), then cease feeding and reduce their metabolic rates during their spawning migrations, due to limited metabolic scope that precludes the simultaneous oxygen demands for spawning and feeding (Rijnsdorp & Ibelings 1989). Although no study has yet investigated temporal variation in feeding levels or metabolic rates among the 3 sub-stocks studied here, the timing of otolith edge deposition in North Sea plaice varies by the area of capture, in relation to the interruption of somatic growth in winter (Van Neer et al 2004). Several studies (e.g.…”

“…6), we were able to confirm the broad timing of deposition of the opaque and translucent bands, irrespective of the sub-stock. Indeed, otolith samples taken at the translucent to opaque transition (deposited in LW/ES, Van Neer et al 2004) (Table 1), 1 from each migration type (see legend for spawning locations, defined in Fig. 1) O as a natural tag (Fig.…”