IMPLICATIONS AND FUTURE DIRECTIONS Ecological implications

1) I have quantified the depth preference of adult/large bodied Greenland halibut and Arctic skate and provided tangible results of the temperature range they occupied.

2) I have provided evidence for a seasonal movement of Greenland halibut, which is in agreement with historic fishery observations.

3) I have examined the relationship between depth and diel cycles for Arctic skate and Greenland halibut.

4) I have described the activity levels of Greenland halibut and Arctic skate and suggested potential explanations for the difference observed in the two species.

Technical implications

1) I have gathered data from PAT tags deployed on fish that inhabit harsh and extremely deep environments, testing PAT tags successful in such

environments.

2) I have evaluated the performance of PAT tags in the Arctic environment from the rate of return of data that were collected.

3) I have confirmed the suitability of the attachment method for Greenland halibut and suggested the use of an alternative attachment method for Arctic skate.

Potential management implications

1) I showed that Greenland halibut exhibited high site fidelity to the deep water area in the central part of Cumberland Sound during the ice free period of the

boundary between the two fishery management areas runs through this deep water area.

2) I provided supporting evidence for the seasonal movement of Greenland halibut in Cumberland Sound, although only two fish reported data for 300 days. Halibut are likely more dispersed during the winter (ice covered period) than the summer.

3) I confirmed that both species overlapped large portions of their habitats, thus management measures addressing the issue of Arctic skate bycatch need to be developed, especially considering that the number of groundfish fisheries in the Arctic may increase in the future.

Potential responses to climate change and implications for fishery management

1) I showed that the distribution of Greenland halibut throughout Cumberland Sound may fluctuate over the course of a year with a wider distribution throughout shallower waters when ice is present to the stock being

concentrated in deep water regions during the ice free season. Thus, changes in the sea ice cycles may have an effect on the distribution patterns of Greenland halibut. For example, a prolonged ice free season may result in longer occupancy of deep water regions by halibut and also longer availability to the open water fishery efforts. Considering that the stock may be confined to relatively limited areas during this period, the local fishery management should consider separate quotas for summer and winter fisheries to secure sustainable harvest.

2) If the water temperature in Cumberland Sound increased as a response to global warming, this might result in Cumberland Sound becoming a

potentially suitable region for Greenland halibut to spawn. If spawning in the Sound, the halibut population may become less dependent on immigrants from Davis Strait and other areas in order to maintain a stable population. However, considering that halibut larvae are usually pelagic that may drift vast distances before settling down and relatively unknown rate of homing of Greenland halibut, it is not clear what effect spawning will have on the stability of the local population.

3) Additionally, changes in climate may bring new species into the area and further disrupt the current dynamics of the current food web, for example by decoupling of food resources. Generalist feeders such as Greenland halibut and Arctic skate that are flexible to feed on a variety of species may be better equipped to face such changes.

Future directions

In conclusion, this study was one of the first to use pop-off archival transmitting tags to successfully monitor the movements of deep water fish species in the Arctic marine environment. Thus, this study showed the practical use of this technology in distant and extremely harsh environments. Furthermore, we increased the current body of knowledge regarding the movement and behavioural patterns of two species that are directly affected by commercial fisheries. This will enable better, more knowledgeable decision making in the future management and conservation practices regarding these

So what would be the next step? This study represents a good starting point for better understanding the environmental preferences, movement and behaviour of two deep dwelling fish species, Greenland halibut and Arctic skate. However, the pop-off archival transmitting technology has limitations that leave certain aspects of our research objectives unanswered. First, the data from the tags cannot be used to quantify fine-scale horizontal movement when species occupy waters beyond the level of light penetration, which is the case for both Greenland halibut and Arctic skate. Secondly, if not recovered, the tags only transmit a certain fraction of the collected data set, which makes the data management challenging and unsuitable for some of the standardized analyses of time series data (e.g., Fourier analysis). Thirdly, the cost of the tags is generally a limitation to an ideal sample size. Lastly, the memory capacity of the tag constrains the data collection to a period of a year or shorter. In terms of the life span of these species, this time period is still rather short and may not represent the full set of movement and behavioural patterns. Thus, despite the information provided by PAT tags being powerful and applicable, future work should consider a number of additional techniques such as

acoustic telemetry and stable isotopes to better define the movement of Greenland halibut and Arctic skate. These methods would enable future research to tackle the remaining research objectives and draw firmer conclusions.

First, the results reported in this study should be compared to data that is currently being collected by acoustic equipment deployed in Cumberland Sound since 2010. These data should help elucidate the extent and timing of the horizontal movement of the two species. Next, to determine if predation is driving the movement of Greenland halibut or Arctic skate, these results should be compared to the movement of the top predators in

the Cumberland Sound system, (i) Greenland shark that were tagged with both PAT and acoustic tags concurrently with the tagging of the two study species (Fisk et al. 2012) and, (ii) beluga whale and its known seasonal movements within Cumberland Sound (Kilabuk 1998). Secondly, results from the stable isotopes analyses of tissues collected in August 2010-11 for both species should be compared to other stable isotope studies conducted in Cumberland Sound on, capelin (Mallotus villosus), shrimp (Lebbeus

polaris) (Dennard et al. 2009), beluga whale (Marcoux et al. 2012), Greenland shark

(McMeans et al. 2010), and ring seal (Pusa hispida) (Dave Yurkowski, University of Windsor, Windsor, ON, personal communication). Comparison of all these results will determine trophic relationships, pinpoint foraging strategies and provide insights into movement and habitat use of Greenland halibut and Arctic skate in the Cumberland Sound ecosystem.

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