Evaluating Age Determination and Spatial Patterns of Growth in Red Sea Urchins in Southeast Alaska

Abstract

The goals of this study were to characterize growth of the commercially harvested red sea urchin Strongylocentrotus franciscanus in southeastern Alaska and test the validity of an aging technique. We aged urchins by counting growth rings on a part (rotula) of the Aristotle's lantern complex from urchins collected at three sites. A subset of collected urchins had three or more years of size measurements from passive integrated transponder (PIT) tag data, allowing us to fit and compare PIT tag and ring-derived growth curves and test the assumption that rings were formed annually. Growth from PIT-tagged individuals approximated the growth derived from ring counts for two of three sites. The third site deviated slightly from predicted growth, providing support for our aging technique. However, we failed to detect any extremely old urchins, suggesting that this technique is not appropriate for assessing the longevity or growth trajectory of very large urchins. An additional five sites without PIT-tagged urchins were sampled to examine spatial variation in growth. Estimates of time to fishery entry varied substantially among sites, but four nonlinear growth functions produced similar estimates at individual sites. Time to fishery entry was positively correlated with an index of food availability, which suggests that the technique revealed true variation in growth rates.

Growth model selection for the jumbo squid Dosidicus gigas from the Gulf of California, Mexico

“…Therefore, the shapes and AIC values can be very close or equal. Similar results have been previously described using the general model of Richards or Schnute vs. different growth submodels (Rogers-Bennett et al 2007, Flores et al 2010, Shelton et al 2006, Barreto et al 2011. The literature shows that for the multi-model inference approach applied to individual growth, it is not unusual that different candidate growth models yield equal values of AIC (Rogers-Bennett et al 2007, Flores et al 2010, Helidoniotis et al 2011).…”

“…The literature shows that for the multi-model inference approach applied to individual growth, it is not unusual that different candidate growth models yield equal values of AIC (Rogers-Bennett et al 2007, Flores et al 2010, Helidoniotis et al 2011). Several studies also have shown that the AIC estimates of the candidate growth models were very close; the magnitude of the change can be < 0.1 (Araya & Cubillos 2006, Shelton et al 2006, Farrell et al 2010, Barreto et al 2011, Grist et al 2011, Mercier et al 2011, Shuman et al 2011. Markaida et al (2005), using mark-recapture data of D. gigas, showed that the daily growth rate diminishes for older individuals; their study analyzed squid between 46 and 80.7 cm ML, and the daily growth rate changed from 1.5 to 1.0 mm d −1…”

“…In our study, the asymptotic growth model identified for D. gigas was based on multimodel inference; this approach is accepted for age and growth modeling as the best statistical procedure for model selection. This approach has been used in age and growth studies of other taxa, such as echinoderms (Shelton et al 2006, Flores et al 2010, fish (Araya & Cubillos 2006, Alp et al 2011, Barreto et al 2011), crustaceans (Montgomery et al 2010) and other mollusks (Rogers-Bennett et al 2007, Cruz-Vásquez et al 2012.…”

Echinoderm Responses to Variation in Salinity

“…These tags allowed identification of individuals held in a single tank and have been used successfully in studies of sea urchins (Hagen, 1996;Shelton et al, 2006). These tags allowed identification of individuals held in a single tank and have been used successfully in studies of sea urchins (Hagen, 1996;Shelton et al, 2006).…”

Evaluation of passive integrated transponder (PIT) tags in studies of sea urchins: caution advised

“…Laboratory studies have demonstrated the potential of PIT tags in measuring growth and survival, without detectable adverse effects, in 2 species of sea urchin: Strongylocentrotus droebachiensis (Hagen 1996) and Evechinus chloroticus (Woods & James 2005). However, the use of PIT tags in field studies has largely been tempered by the lack of underwater readers (Duggan & Miller 2001), and is limited to 2 studies of growth and age determination (RogersBennett et al 2003, Shelton et al 2006. Recently, the development of smaller and more independent readers, which can be encased in a waterproof housing, has permitted their usage underwater.…”