Using acoustic telemetry to observe the effects of a groundfish predator (Atlantic cod, Gadus morhua) on movement of the American lobster (Homarus americanus)

Abstract

American lobster (Homarus americanus) landings have more than quadrupled in the last two decades , coinciding with the collapse of Gulf of Maine groundfish fisheries such as Atlantic cod (Gadus morhua). Recently there has been speculation that the release of lobster from predatory control may have resulted in both lower predation rates and increased foraging areas. We used fine-scale acoustic telemetry within a 200 m × 250 m field enclosure to test the hypothesis that cod induce lobsters to decrease movement and seek refuge. We found a large amount of variation in the behavioral response of individual lobsters to predators; however, the addition of cod into the enclosure reduced maximum daily home range area and significantly reduced the distance traveled from shelter habitat area for all individuals. When predators were removed from the enclosure, lobsters responded by increasing home range area and significantly increasing the distance traveled from shelter habitat area. These results represent the first experimental evidence for American lobster range contraction and subsequent expansion in the presence and absence of cod, respectively.Résumé : Les débarquements de homards (Homarus americanus) ont plus que quadruplé au cours des deux dernières décennies , coïncidant avec l'effondrement des pêches aux poissons de fond, comme la morue (Gadus morhua), dans le golfe du Maine. Il a récemment été proposé que la disparition du contrôle des homards par la prédation puisse s'être traduite par des taux de prédation réduits et de plus grandes zones d'alimentation. Nous avons utilisé la télémétrie acoustique de haute résolution dans un enclos en mer de 200 m sur 250 m pour vérifier l'hypothèse voulant que la morue incite les homards à restreindre leurs déplacements et à trouver refuge. Nous avons noté d'importantes variations en ce qui concerne la réaction comportementale individuelle des homards à la présence de prédateurs; cela dit, l'ajout de morues dans l'enclos a entraîné une diminution de la superficie maximum du domaine vital quotidien et une diminution significative de la distance des excursions en dehors de la zone d'habitat refuge pour tous les individus. Quand les prédateurs étaient retirés de l'enclos, la superficie du domaine vital des homards augmentait et la distance des excursions en dehors de la zone d'habitat refuge augmentait significativement. Ces résultats constituent les premières preuves expérimentales de la contraction du domaine vital du homard en présence de morues et de son expansion en leur absence. [Traduit par la Rédaction]

Fine-scale movement, activity patterns and home-ranges of European lobster Homarus gammarus

“…Recent advances in acoustic telemetry (AT) tracking techniques offer an innovative means of near continuous in situ observation, with minimal disturbance to the animal. These technologies have begun to produce novel insights into clawed lobster behaviour (MacArthur et al 2008, Moland et al 2011a, McMahan et al 2013a. AT reduces the re liance upon baitedtraps, which are constrained by issues of variable effort, catchability and trap saturation; these issues have historically hindered the robustness of findings.…”

Ecological and socioeconomic implications of a northern range expansion of black sea bass, Centropristis striata

“…Despite the relatively brief time in which these populations have geographically overlapped, lobsters from midcoast Maine (Mid) recognized and responded to sea bass as they would to native fish predators, such as sculpin and Atlantic cod (Wahle 1992, McMahan et al 2013, Wilkinson et al 2015. Furthermore, Downeast (DE) lobsters consumed significantly fewer mussels in the presence versus absence of sea bass, indicating that they too were able to recognize and respond to a novel predator.…”

“…Other potential predators such as cusk (Brosme brosme) and Atlantic wolffish (Anarhichas lupus) are also at low biomass levels (AWBRT 2009, NEFSC 2006. The drastic decline in cod and other top predator stocks over the past several decades has altered the GOM food web, resulting in increased mesopredator populations such as cunner (Tautogolabrus adspersus) and sculpin (Myoxocephalus scorpius) (Witman andSebens 1992, Steneck 1997), and has even been linked to influencing American lobster (Homarus americanus) populations (McMahan et al 2013). The functional absence of many of the GOM's top predator may similarly be allowing black sea bass to expand into new territory with little top-down control exerted on their population.…”

“…The degree to which the northward expansion of black sea bass is affecting lobster populations is unknown; however, fish predators can reduce lobster movement and foraging behavior and may potentially influence lobster population dynamics (Wahle 1992, Spanier et al 1998, McMahan et al 2013, Wilkinson et al 2015. Therefore, there may be both ecological and socioeconomic impacts of the recent increase of black sea bass in the GOM.…”

“…Furthermore, Selden et al (2016) found that a recent contraction in the southern range limit of lobsters was correlated with the northern expansion of sea bass. Because predatory fish induce strong NCEs in juvenile lobster populations, such as increased shelter usage and reduced foraging (Wahle 1992, Spanier et al 1998, McMahan et al 2013, Wilkinson et al 2015, the expansion of this aggressive fish predator into the GOM could have substantial ecological and socioeconomic impacts.…”