Posts

Impact of Multiple Stressors on Sea Bed Fauna in a Warming Arctic

/in , /by

By: Brenna Bales, SRC Intern

The Arctic Ocean has been a heavily monitored area in recent years as climate change continues to affect the planet. This area is at high risk due to the fact that is has warmed at almost twice the rate as the rest of the planet in recent decades causing a decrease in sea-ice cover, glacial volume, and increases in temperature and precipitation (Hassol and Corell 2006). The Barents Sea is particularly vulnerable to climate change as it is experiencing the greatest temperature increases throughout the Arctic and may soon become an Atlantic-dominated climate region with warm and well-mixed waters, further preventing sea ice formation (Lind et al. 2018). Jørgensen et al. (2019) examined the Barents Sea benthic (seafloor) composition and how it has been affected by several stressors relating to climate change. Ecological impacts among the benthic environment were examined as a result of seawater warming, bottom trawling, and predation from a new, invasive predator: the snow crab (Figure 1).

Figure 1: Two snow crabs along the seafloor, a larger male above and a smaller female below. Image Credit: Derek Keats, Johannesburg, South Africa

The study characterized the vulnerability of different invertebrate groups when affected by these three variables across a predefined grid consisting of 36 x 36 nautical mile cells in the Barents Sea (Figure 2). Firstly, sensitivity to seawater warming between 2009-2011 (colder period) versus 2012-2015 (warmer period) was investigated. Both species temperature indices (a measure of the average temperature experienced by individuals across a species’ range) and community temperature indices were calculated by combining temperature values with information about the seafloor organism distribution. Secondly, species vulnerability to bottom trawling (Figure 3) was characterized by a species’ morphology, mobility, and body size. Slower, larger, and taller animals were categorized as having a larger susceptibility to trawling effects, whereas quicker, smaller animals would be more resilient. Lastly, the predatory effects of the invasive snow crab were quantified by number of prey items and annual biomass (amount of prey) consumed.

Figure 2: Geographic location of the Barents Sea with the 2280 sampling locations from the present study (Jørgensen et al. 2019).

Figure 3: Depiction of the practice of bottom trawling (Source: NOAA.gov).

From the initial, colder period (2009-2011) to the latter, warmer period (2012-2015), there was an increase in organisms with warm-water affinities and a reduction in those with cold-water affinities. While the overall sensitivity to temperature of the communities decreased with time, areas that were further north into the Arctic showed a higher vulnerability to temperature changes than more southern areas continuously experiencing warming waters. The sensitivity to trawling was lowest in the center region of the Barents Sea and increased toward outer regions. Lastly, the sensitivity to snow crab predation was highest along the northwestern border connecting to the southeastern border of the study area. Overall, the northwestern area of the Barents Sea was found to be the most vulnerable area when all three variables were combined. In conclusion, the combination of multiple stressors in any particular area can have severe consequences on the resilience of a local community to change. Management in the form of closed areas or gear modification is thus highly recommended by researchers from this paper to lessen the threats that these communities, especially those of the northwestern Barents Sea, are facing.

Work Cited:

Hassol, S.J. and Corell, R.W., 2006. Arctic climate impact assessment. Avoiding dangerous climate change, p.205.

Jørgensen, L.L., Primicerio, R., Ingvaldsen, R.B., Fossheim, M., Strelkova, N., Thangstad, T.H., Manushin, I. and Zakharov, D., 2019. Impact of multiple stressors on sea bed fauna in a warming Arctic. Marine Ecology Progress Series, 608, pp.1-12.

Lind, S., Ingvaldsen, R.B. and Furevik, T., 2018. Arctic warming hotspot in the northern Barents Sea linked to declining sea-ice import. Nature Climate Change, 8(7), p.634.

Addressing knowledge gaps to utilize best practice management for bottom-trawling fisheries

/0 Comments/in , /by

By Grace Roskar, SRC Intern

Bottom-trawls are a type of fishing gear that can be destructive towards the seabed and its associated organisms. A fishing vessel tows large trawl nets that trap marine animals as they are dragged across the ocean floor. With heavy ropes, chains, or bars, the fishing gear disturbs the seabed while capturing nearly anything in its path. About 20% of fish and shellfish caught globally every year are caught using bottom-trawls, amounting to about sixteen million tons.

A typical bottom trawl. Source: https://commons.wikimedia.org/wiki/File%3ABenthictrawl.jpg

A typical bottom trawl. Source: https://commons.wikimedia.org/wiki/File%3ABenthictrawl.jpg

A meta-analysis by McConnaughey et al., in 2005 has shown that bottom trawling for benthic invertebrates may cause reductions in a decrease in biomass, the diversity of fish, and the body size of fish, among other ecological traits of fish communities. Some fish species use specific habitats for shelter or food, and it may be possible that trawling and dredging impact the productivity of these fish species. This is especially important to examine because wild-capture fisheries provide a substantial amount of food for the growing global population.

This study aimed to identify specific questions about bottom-trawling fisheries that key stakeholders feel need to be scrutinized in order to guide suitable policy and management measures. The research also sought out important gaps in global knowledge that, if taken into consideration, would help the advancement of best practice management for bottom-trawling fisheries, defined as ‘bottom trawling that would achieve sustainable fisheries production while minimizing adverse impacts on the environment’ (Kaiser et al 2015).

First, a group of 52 stakeholders from 11 different countries was selected. Stakeholders were categorized either as research scientists or practitioners, a group that comprised of people from fishing and processing industries, non-governmental organizations, or governmental organizations. The stakeholders composed a comprehensive list of ‘knowledge-needs’, which were then voted on and ranked in terms of priority. The underlying idea was that addressing these knowledge-needs would be necessary to support the development of best practice management. Through a one-day workshop, including discussion sessions and voting, a list of 25 top-priority knowledge-needs were finalized out of the original 108.

This flow diagram shows the methods of prioritizing knowledge-needs into a final list.

This flow diagram shows the methods of prioritizing knowledge-needs into a final list.

Several statistical tests were used to examine how the reasoning behind the rankings varied between practitioners and scientists. The median scores were positively correlated for each knowledge-need, showing high agreement levels between the scientists and practitioners of what was top priority. Knowledge-needs were organized into categories: direct effects, ecosystem and production, operational, and management and indicators. The management and indicators category was the most represented, with six knowledge-needs in the top ten. The highest-ranked knowledge need was ‘What is the extent and distribution of different seabed habitat types?’ Given the wide range of different stakeholders consulted, the agreement between the scientists and practitioners about the importance of this knowledge-need is encouraging. It shows the pressing need to better understand the relationship between bottom-trawling and the different habitat types affected. Furthermore, six other knowledge-needs were related to some extent to improving knowledge of the impacts of interactions between fishing gear and the seabed. The second most highly ranked question asked, ‘What level of trawl fishing impact on other ecosystem services is acceptable such that sustainable seafood production can be maintained?’ This question suggests that the environmental impacts of bottom trawling, such as changes in ecosystem structure and the fish population, need to be evaluated in comparison to the social and economic impacts of trawling.

A list of the top ten knowledge-needs, including what category each was placed in.

A list of the top ten knowledge-needs, including what category each was placed in.

The rest of the knowledge-needs addressed a range of topics, from the need for better understanding of where bottom trawling occurs and how much of it, to evaluating the ability of certain habitats to recover from the effects of trawling. Many knowledge-needs were additive, such that addressing one would help advancement to another. The study successfully identified specific questions that will be collaboratively discussed further to close knowledge gaps in the global fisheries industry. Future research would include continuing to examine collective knowledge and to use discussion to work towards closing knowledge gaps.

 

References: 

Kaiser, M. J., et al. (2015). “Prioritization of knowledge-needs to achieve best practices    for bottom trawling in relation to seabed habitats.” Fish and Fisheries.      doi: 10.1111/faf.12134

McConnaughey, R. A., and Syrjala, S. E. Short-term effects of bottom trawling and a storm event on soft-bottom benthos in the eastern Bering Sea. – ICES Journal of            Marine Science, 71: 2469–2483.