Behavioural consequences of density-dependent habitat use in juvenile cod Gadus morhua and G. ogac: the role of movement and aggregation

The protection of species requires an understanding of their habitat requirements and how habitat characteristics affect their distribution, survival and growth. This need is especially important in areas where anthropogenic pressures can not only have a significant direct impact on the survival of the species but also damage their habitat. The Firth of Clyde in southwestern Scotland was an important commercial fishing area for a variety of demersal fish species up until 1973. However, stocks rapidly declined thereafter and the catch of targeted species ceased in 2005, despite fisheries measures put in place to aid recovery. Changes in the availability and quality of fish habitat are possible explanations for this lack of recovery. Here, we report on stereo baited remote underwater video surveys in the Firth of Clyde between June and September in 2013 and 2014 to determine the habitat of juvenile Atlantic cod Gadus morhua, haddock Melanogrammus aeglefinus and whiting Merlangius merlangus. Habitat predictor variables explored included substratum type, depth, wave fetch, and epibenthic and demersal fauna diversity. G. morhua were most abundant in shallow, sheltered areas composed of gravel−pebble containing maerl. M. aeglefinus and M. merlangus predominated over deeper sand and mud. Ontogenetic shifts in all 3 species were also observed. Relative abundances of G. morhua and M. merlangus were positively related to the diversity of epibenthic and demersal fauna. Our results indicate that spatial conservation measures to benefit demersal fish should be advised by patterns of epibenthic and demersal fauna diversity as well as physical substratum types.

Section: Discussionmentioning

confidence: 61%

Section: Introductionmentioning

confidence: 99%

Juvenile gadoid habitat and ontogenetic shift observations using stereo-video baited cameras

Elliott¹,

Turrell²,

Heath³

et al. 2017

“…Massot et al 1994). To date there have been few explicit tests of DDHS in marine fish species (juvenile pollock Pollachius virens, Rangley & Kramer 1998; juvenile cod Gadus morhua and G. ogac, Laurel et al 2004; gag Mycteroperca microlepsis, Lindberg et al 2006) despite the multitude of studies describing area-abundance relationships in marine environments (see Shepherd & Litvak 2004 for review). In flatfish, fine grained sand substrates are preferred over relatively coarser grained substrates (Stoner & Ottmar 2003), most likely because flatfish are more capable of burying in such habitats as a means of reducing predation (Ryer et al 2004; although see Manderson et al 2000) or finding food (Livingston 1987).…”

Section: Density-dependent Habitat Selectionmentioning

confidence: 99%

“…Marshall & Frank 1995, Hutchings 1996, Blanchard et al 2001. Habitat suitability is a dynamic measure mediated by behavior (Laurel et al 2004), ontogeny (e.g. Livingston 1988) and the environment (e.g.…”

Section: Introductionmentioning

confidence: 99%

Density-dependent habitat selection in marine flatfish: the dynamic role of ontogeny and temperature

Laurel¹,

Stoner²,

Hurst³

2007

Self Cite

Changes in habitat use with increasing conspecific density are well-documented, but such patterns are likely to be dynamic over the lifespan of the organism and responsive to changes in the environment. In the laboratory, we examined how habitat selection was mediated by ontogeny (6, 8 and 12 mo) and temperature (4 and 9°C) in 2 juvenile, marine flatfish species: Pacific halibut Hippoglossus stenolepis and northern rock sole Lepidopsetta polyxystra. In a set of initial trials at 9°C, groups of same-aged juvenile flatfish (6, 8 or 12 mo) of either halibut or rock sole were given the choice of 2 habitats -fine sand (preferred) and coarse gravel (unpreferred) -at 1 of 6 densities (0.4 to 12.2 fish m -2 ). A second set of trials was conducted at 4°C using 8 mo juvenile fish of both species over the same range of densities. At 9°C, density-dependent habitat selection was observed among all treatment groups. As juveniles increased in age in the 9°C treatments, both species began occupying the less-preferred gravel habitat at lower densities. However, at 4°C, density-dependent habitat selection varied between species. Sand habitat supported higher densities of juvenile Pacific halibut at 4°C whereas no change was observed in northern rock sole. Juvenile Pacific halibut activity was also lower than rock sole at 4°C, suggesting that competitive interactions (e.g. interference, territoriality etc.) and/or physiological demands of halibut is sufficiently reduced at this temperature to increase the carrying capacity of the preferred habitat. Together, these results indicate that temperature, ontogeny and density interact to yield unique habitat selection patterns in fish, mechanisms that may be important in area-abundance relationships.KEY WORDS: Density-dependence · Habitat selection · Carrying capacity · Pacific halibut · Northern rock sole Resale or republication not permitted without written consent of the publisher

“…Published accounts of the more extensively studied Atlantic cod describe movements of older individuals over both space and time through mark-recapture methods (Grant & Brown 1998b, Laurel et al 2004, Robichaud & Rose 2004 and acoustic telemetry (Cote et al 2004, Lindholm et al 2007. At the juvenile stage, Greenland cod exhibit demersal habitat use and behaviour similar to juvenile Atlantic cod (e.g.…”

Section: Introductionmentioning

confidence: 99%

Season and site fidelity determine home range of dispersing and resident juvenile Greenland cod Gadus ogac in a Newfoundland fjord

Shapiera¹,

Gregory²,

Morris³

et al. 2014

Self Cite

We used acoustic telemetry to track age 1 juvenile Greenland cod Gadus ogac in Newman Sound, Newfoundland, from October 2010 to November 2012, in 2 consecutive 1 yr experiments. Using single (Year 1) and reciprocal (Year 2) transplant study designs, we investigated seasonal dispersal, home range area, and potential homing behaviour between coves 3.5 km apart. We tracked individuals moving at metre to kilometre scales, using a network of 26 to 32 hydrophones. We converted tag detections to position estimates in order to calculate seasonal home ranges and individual movement patterns. Home range increased significantly with season (pre-winter, winter, and post-winter) in both study years. Mean seasonal home range area ranged from 0.29 to 3.47 km 2 in Year 1 and 0.43 to 1.72 km 2 in Year 2. In contrast, fish size-at-capture, capture location, and release location had no significant effect on seasonal home range. Increased movement distance during the winter and post-winter season suggests a reduction in predation pressure on age 1 juveniles at these times, challenging previous assumptions about their vulnerability. We observed variable behaviour spanning residency to kilometre-scale dispersal movements, which represent greater distances than previously assumed. Similar proportions of control and transplant fish visited the other cove, indicating an absence of homing behaviour among dispersing individuals. Juveniles of marine fishes are often characterized as key life history transition stages between vulnerable larvae and older, larger individuals which are less susceptible to predators. Our results indicate that early juvenile life stages may be substantially more mobile than presupposed and contribute to population connectivity in temperate fishes in ways not well described previously.