The geography and bathymetry of American lobster benthic recruitment as measured by diver-based suction sampling and passive collectors

Abstract

We present results of an international collaboration to survey American lobster Homarus americanus Milne-Edwards, 1837 nurseries in Atlantic Canada and the northeast United States from 2007 to 2009 under a standardized protocol involving two sampling methods, diver-based suction sampling and passive collectors. We surveyed young-of-year and older juveniles at 191 sampling sites over 39 sampling areas considerably expanding the known depth range and geographic limits of benthic recruitment. Young-of-year densities were strongly correlated in space with the abundance of older juveniles, signifying consistently strong settlement in the Gulf of Maine, lower Bay of Fundy, southwestern Nova Scotia and southern Gulf of St. Lawrence, and relatively weak settlement in southern New England, eastern coastal Nova Scotia and Newfoundland, a pattern consistent with commercial lobster harvests. Passive collectors elucidated bathymetric patterns of young-of-year recruitment in oceanographically contrasting regions. Although we observed young-of-year lobsters as deep as 80 m, they were most abundant above the thermocline in summer-stratified regions, such as the western Gulf of Maine and southern New England, and depth-wise differences were less extreme in thermally mixed waters of the eastern Gulf of MaineÁFundy region, a finding consistent with previous observations that postlarvae concentrate above the thermocline. Between the two samplers, we detected no sampling bias for young-of-year lobsters, although collectors may slightly underrepresent older juveniles entering from the surrounding sea bed. Finally, we found that interactions between juvenile lobsters and suspected predators or competitors in collectors, such as crabs and fishes, are weak and unlikely to bias collector results.

Effect of background substrate on recruitment of benthic marine invertebrates to subtidal cobble-filled collectors

“…Although the lobster shows a strong preference for cobble substrate for settlement (Botero and Atema 1982;Wahle and Steneck 1991), it appears to continue to settle in cobble (like that in the collectors) regardless of the substrate heterogeneity of a site, at least at the spatial scale and substrate patchiness examined in our study. This finding for lobsters is of particular interest because scientists have been using these collectors to quantify and monitor lobster settlement in different parts of the USA and Atlantic Canada (Wahle et al 2013). However, it is quite likely that larger patches of less suitable sediment habitat might influence lobster larval behaviour and reduce settlement.…”

Spatial linkages between settling young-of-year and older juvenile lobsters

“…The index has been collected over a broad spatial scale in New England, USA, and provides a powerful resource to evaluate settlement patterns and suggest mechanisms that may influence recruitment dynamics in this species (e.g. Wahle et al 2013). In a related study, we showed a strong correlation between lobster settlement and the occurrence of older juveniles in collectors and suction samples over scales of 1 to 10 km (Wahle et al 2013).…”

“…Wahle et al 2013). In a related study, we showed a strong correlation between lobster settlement and the occurrence of older juveniles in collectors and suction samples over scales of 1 to 10 km (Wahle et al 2013). Here, we expand on that work to identify the underlying mechanisms and relevant spatial scales driving that correlation.…”

“…Given the dependence on cobble-boulder habitat for the first few years of life, settlement strength is a major determinant of older juvenile abundance in cobble nurseries (Wahle et al 2004(Wahle et al , 2013. Although juveniles outgrow this habitat dependence and emerge from nurseries after several years, the degree to which resident conspecifics promote or deter settlement of new cohorts remains unknown.…”

Lobster research integrated: From biology to management

“…The first of four contributions on the American lobster H. americanus demonstrates the fine structure of the lobster's cuticle as an interface to the environment Marine Biology Research, 2013; 9: 3Á6 (Kunkel & Jercinovic 2013;contr. 3) followed by a paper on intraspecific recognition and communication (Gherardi et al 2013;contr. 4) leading to an encompassing study of benthic recruitment (Wahle et al 2013;contr. 5) and concluding with a behavioural study which has consequences for sampling and population assessment (Watson & Jury 2013;contr.…”