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

Abstract

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.

Seabed Habitat Determines Fish and Macroinvertebrate Community Associations in a Subarctic Marine Coastal Nursery

“…Coastal-zone fish communities varied both seasonally and among seabed habitats in this study. Influences of temperature on distribution and behavior are well documented among poikilotherms, both globally (Fretwell 1972) and locally (e.g., Shapiera et al 2014). Seasonal effects on community associations were significant, as we expected a priori, and these were consistent with expectations from demonstrated causal relationships (Adams 1976), possibly due to metabolic rates (Clarke and Johnston 1999) or ontogenic shifts in habitat association (Kimirei et al 2011).…”

Contrasting intra-individual variation in size-based trophic and habitat shifts for two coastal Arctic fish species

“…Given that RBC has a maximum turnover rate of several weeks, the trophic shift observed across all body sizes could be due to increasing local availability of lower trophic level prey during and immediately after spring ice-breakup (Hansen et al 2012 ). The dichotomous shift for some individuals could be due to partial feeding migrations of specialists within a generalist population, similar to coastal Atlantic cod (Meager et al 2018 ), and Greenland cod over small scales at lower latitudes (Morin et al 1991 ; Westrheim 1996 ; Shapiera et al 2014 ). The positive effect of phase angle on δ 13 C-body size regressions (both plasma and RBC) in Greenland cod, and δ 15 N-tissue differences in Arctic char suggests that ontogenetic habitat shifts in Greenland cod and trophic shifts in Arctic char may be important for maintaining body condition at larger sizes.…”

Applying Movement Ecology to Marine Animals with Complex Life Cycles

“…For our purposes, we discuss juvenile and adult movements collectively as adults, but note that this simplification is more appropriate for some species than others. Moreover, although new tagging technologies provide significant insights into adult movement (Block et al 2011) (see below), the small size of juveniles precludes their use except in larger individuals (e.g., Shapiera et al 2014), limiting knowledge of how juvenile and adult movement ecologies may vary beyond movements related to reproduction.…”

“…In fish, real-time tracking tools, such as radio telemetry and GPS, can detect subtle spatial and temporal changes in speed, velocity, acceleration, and direction and environmental variation, and can generate high-resolution maps of individual movement paths and habitat usage (e.g., Lamare et al 2009, Kessel et al 2014, Shapiera et al 2014. Modeling techniques can integrate such information to match an observed change in a movement step or phase to changes in internal and environmental states (Patterson et al 2008).…”