Sea-ice loss boosts visual search: fish foraging and changing pelagic interactions in polar oceans

By Nicole Suren, SRC Intern

Light availability is one of the most important factors in the success of visual foraging. It can be controlled by many variables such as turbidity or weather, but in polar ecosystems ice cover and seasonality are the primary controls for light availability. Climate change has had and will continue to have a huge effect on polar ecosystems through temperature and weather changes, but one of the most notable side effects examined in this study is how increased light availability caused by receding ice and reduced snow cover will affect the success of polar visual foragers. The study modeled the success of planktivorous, visually foraging fish, with the underlying principle of the model being that increased ambient light will increase visual range, thereby making prey detectable at a larger distance and increasing foraging efficiency. The results showed that declines of polar sea ice would boost the visual search of planktivorous fish, but only seasonally. While light availability related to ice cover can be variable due to climate change, the long dark periods caused by polar seasonality are factors independent of climate, and therefore will still place limits on visual foraging during those seasons.

Figure 1

(a) The blue line shows how sea ice extent has decreased over the past decades, and below is a diagram demonstrating that prey will become more likely to be visually detected as the thickness of sea ice decreases. (b) A variety of factors influence prey detection, including the nature and angle of incoming light. Predator, prey, and visual range are not drawn to scale. (Langbehn & Varpe, 2017)

The models predict that several things will change due to light availability caused by loss of ice cover. First, primary productivity may increase, depending on nutrient availability. Second, seasonal feeding migrations into the poles are expected due to the removal of the limiting factor of lack of light for visual foragers. This prediction has already been verified by real-world data; increased feeding forays by Atlantic Salmon, Atlantic Mackerel, and Atlantic Herring have been recorded, and these coincide with decreasing ice cover over the past 35 years. More generally, mobile, fast-swimming predators are predicted to take advantage of these foraging opportunities the most. However, increased light availability can also increase the likelihood of planktivorous predators being spotted and predated upon by larger visual predators in a higher trophic level. This means that not only will the ideal user of these seasonal foraging grounds be mobile and fast-swimming, but they will either be apex predators or schooling fish, which can use the technique of schooling to forage in relative safety despite being visible.

Figure 2

The extent of sea ice is averaged from 2010-2015 in (a) and (b), and (c) and (d) show how visual range correlates with these averages. Data from the Bering Sea and the Barents Sea are shown. (Langbehn & Varpe, 2017)

No matter how efficiently visual foragers learn to take advantage of increased light availability at the poles during the summer months, the darkness of winter will still be a significant limiting factor in regards to permanent habitat expansion. Polar winters will always be long and dark, even if climate change alters the ice cover in that time. This means that the permanent inhabitants of the poles will likely remain the only permanent inhabitants due to their specialized adaptations for living in darkness, while trophic interactions are likely to change during the summer.

Work Cited

Langbehn, T. J., & Varpe, Ø. (2017). Sea-ice loss boosts visual search: Fish foraging and changing pelagic interactions in polar oceans. Global Change Biology, (November 2016). https://doi.org/10.1111/gcb.13797

Polar Bears are Vulnerable to Loss of Sea Ice

By Rachael Ragen

Figure 1

Polar Bear, https://sealevel.nasa.gov/ system/news_items/main_images/ 74_polarbear768.jpeg

Polar bears are currently facing a major problem: declining sea ice. As greenhouse gases continue to increase due to anthropogenic factors causing temperatures to rise and ice to melt. Since polar bears rely on sea ice as they search for prey, the decline in sea ice makes hunting much more difficult. The current population of polar bears is estimated to be 26,000 with 19 subpopulations in 4 ecoregions (Figure 2). It is very difficult to properly assess each subpopulation of polar bears as they live in extreme environments. Therefore, no global assessment has been done and the status of some subpopulations is unknown. The study by Regehr et al. aimed to look at the effect of sea ice decline on polar bears by determining the generation length, forming a standardized sea ice metric, and then using statistical models and computer simulations.

Figure 2

Map of Ecoregions, Regehr et al.

In order to determine the generation length, the authors looked at the age of female polar bears with a cub and found the average to be 11.5 to 13.6 years. Live capture data was used to determine these numbers. The upper level is used to account for variations in generation length.

A sea ice metric was determined using satellite data from 1979 to 2014. This data was used to establish the carrying capacity, which is the maximum amount of organisms the habitat can support, for the polar bears. Then the value found for K (carrying capacity) was used in linear models. This analysis generated predicted future values of ice as well, as the effect these values had on subpopulations. The ice decline was shown to affect all subpopulations.

The statistical models and computer simulations looked at the relationship between polar bear populations and sea ice over three generations using three different methods. First they assumed that changes in sea ice are directly proportional to changes in subpopulation abundance. This method was useful for populations with limited data. Second they looked at a linear relationship between ice and subpopulation abundance for subpopulations, although data was only available for seven of the nineteen. There was not shown to be a significant change due to variations in the status subpopulations as well as uncertainty in estimates of abundance. Lastly they again looked at a linear relationship between ice and population but for each of the four ecoregions. Some ecoregions showed a significant change, whereas others did not, showing that dynamics and biological productivity varies between subpopulations.

Figure 3

Table of data found, Regehr et al.

This study looked at the IUCN Red List’s guidelines for risk tolerance. The culmination of these studies showed that the first generation’s mean global population size was to decrease by 30%, the second by 4%, and the third by 43% (Table 1). Since there was shown to be a high risk of the population decreasing by 30% and a low chance of the population decreasing by 50% (Table 1), polar bears are classified as vulnerable.

The need for MPAs in the Antarctic

By Haley Kilgour, SRC Intern

With global climate change in effect the Arctic ice sheet has been losing area and has gone from 7.5 million km^2 in 1979 to 4 million km^2 in 2016 (Figure 1). The loss of ice coverage is detrimental to many species, but on the other hand opens up areas to new fishing grounds, oil and gas deposits, deep sea minerals, and shorter shipping routes that were previously inaccessible. While economically it is beneficial to exploit these now accessible resources, it is also necessary to designate Marine Protected Areas (MPAs) to preserve habitat and biodiversity.

Figure 1

Year round see ice cover for the periods of 1979-1984 and 2012-2016.

Geomorphic features such as seamounts, submarine canyons, hydrothermal vents, submarine plateaus, ridges, and escarpments serve as a proxy for benthic communities and ecological processes as they are often areas of high biodiversity and important to processes such as upwelling. Harris et al looked at the distribution of geomorphic features on the sea floor to assess their current level of protection within MPAs. They also aimed to see if these features were occurring within or outside of MPAs and identify ones that were once inaccessible due to year round sea ice.

To determine their area of study, Harris et al used the average minimum sea ice coverage from 1979-1983. They looked at the years 1979-1983 and 2012-2016 (the earliest and latest time periods) to see how much of the geomorphic features are now exposed. Twenty-nine categories of features were mapped using Shuttle Radar Topography Mapping (Shuttle Radar Topography) and MPA boundaries were taken from the IUCN and UNEP-WCMC database. The program ArcGIS was then used to compute areas.

On average, 31% of all previously year round covered features in the Arctic are now in open water in September. In 1979-1983, only 2.33% of areas below year round sea ice were in MPAs, and these were mostly areas on coastal and shelf habitats (Figure 2). This lack of diversity in features that are protected means there is high potential for them to be exploited now that year round ice no longer prevents access.

Figure 2

MPAs within the Arctic in relation to September sea ice cover in the periods 1979-1983 and 2012-2016.

As it stands, only 2.3% of the areas used in this study are in MPAs. While this seems to pose a problem, Canada, Denmark, Russia, Norway, and the USA have signed a “Declaration concerning the regulation of unregulated high seas fishing in the central Arctic Ocean” and a moratorium. Thereby, the areas beyond national jurisdiction have a degree of protection from fishing pressure at the current time.

Current MPAs mostly cover coastlines and inner shelf regions. Abyssal plains are not covered at all and there negligible protection for slope habitats. While the current MPAs do provide a small effect, they are not representative in the standard MPA design.

There are many geomorphic features that have been left exposed and all are fragile ecosystems. Basins collect sediment and anthropogenic contaminants, making them particularly susceptible to pollution from runoff and chemicals. Submarine canyons are considered biodiversity hot spots and prime fishing grounds, making them vulnerable to degradation. Only .2% of canyons are within existing MPAs and retreating sea ice now exposes 37% of their area. Submarine canyons face particular danger because they are associated with oil and gas deposits. Plateaus are mostly unexplored worldwide and thus need further examination and protection.

These underwater geomorphic regions are high in biodiversity but are finding themselves in peril with retreating sea ice. Many of these areas are likely under rapid ecological transition as the Arctic responds to global climate change. These ecosystems are highly unexplored and sensitive. They could be lucrative economically, but are also most likely highly important for conservation. MPAs will play a major role in protecting these areas.

Does marine debris affect tourist perception and tourism revenue?

By Casey Dresbach, SRC Intern

The top worldwide providers of ecosystem services of both leisure and recreation include coastal areas such as beaches and estuaries (Millennium Ecosystem Assessment, 2005). These natural environments are home to hundreds of thousands of marine organisms, all of which require clean domains to flourish, thrive, and grow in. Unfortunately, human pollution has made its way into these areas, as depicted in Figure 1. “Marine debris” can be defined as any solid, persistent, human-created waste that has been deliberately or accidentally introduced into a waterway or ocean from shorelines to the ocean floor (Oregon Coast STEM Hub, 2017). Not only does this breed of debris directly affect marine species ocean-wide, but current research is also showing that it is taking a toll on both tourism and tourists’ destination choices worldwide.

Figure 1

Dr. Sylvia Earle engaging with a Laysan albatross nesting among marine debris. (USFWS – Pacific Region, 2012)

Marine debris is complex in its nature and jeopardizes other coastal entities. The debris has a dual effect on both the marine life as well income generated from local tourism. The interaction between marine debris and tourism is complex because items may form in regions other than the places where the litter is stranded and where tourism occurs (Krelling, Williams, & Turra, 2017). Individuals visiting beaches and coastal regions are more likely so seek alternate destinations if their overall experience is not remarkably enjoyable, and a substantial amount of scattered litter may play into that alternative choice of destination.

The coast of Paraná state in southern Brazil is one of the most frequented tourist destinations in this region (Krelling, Williams, & Turra, 2017). Many tourists, such as second-home owners and users (SHOU) and non-recurrent vacationers, frequent this Brazilian coast. A single SHOU is an individual or group of individuals who have an additional property, or vacation home elsewhere. And a non-recurrent tourist is an individual who has no territorial tie to a destination – is interested in vacation without having loyalty of a piece of land. In a recent study by researchers Allan Krelling, Allan Williams and Alexandra Turra, both the perceptions and reactions of these two distinct groups of beach users were compared. More than 70% of the visitors are SHOU. In fact, some of Paraná’s cities are dependent on property taxes from these second homeowners as well as the expenditures spent by the non-recurrent tourists on services such as food, activities, and other conveniences. Collectively, the two user groups and their tourism revenue drive the economy in the coastal area.

Figure 2

(a) Depicts the entire coastal region of Paraná State in southern Brazil. (Top right) Pontal Do Sul, a highly frequented estuarine beach in the coastal region of southern Brazil. (Bottom right) lpanema, a highly frequented open ocean beach in the coastal region of southern Brazil (Krelling, Williams, & Turra, 2017).)

The study compared both the perceptions and reactions of the two user groups. SHOU and non-recurrent tourists were administered a questionnaire to determine socioeconomic characteristics at two Brazilian sub-tropical beaches: Pontal do Sul and Ipanema, exhibited in Figure 2. Pontal do Sul is an estuarine beach and Ipanema is an open-ocean beach, which is more frequented by non-recurrent tourists. The ultimate goal of the questionnaire was to characterize these beach users’ socioeconomic characteristics such as yearly income, level of education, daily per person expenditure, frequency of trips and period of permanence (Krelling, Williams, & Turra, 2017). The survey also examined perceptions and reactions, especially those regarding the potential negative economic impacts of marine debris. Pontal do Sul and Ipanema were selectively chosen because of their varying geographical characteristics, ultimately adding more variability to the study set.

The general findings showed that SHOU might have a different reaction towards the marine debris than the average tourist. This can be linked to their loyalty to the destination, specifically tied to the property they have there. Results did show, however, that if debris were to reach a significant amount (>15 items/m2), more than 85% of beachgoers would look elsewhere when searching for a coastal region to vacation (Krelling, Williams, & Turra, 2017). If this were the case the stranded litter would threaten the Brazilian economy by reducing local tourism income by 39.1%, (Krelling, Williams, & Turra, 2017) which would present losses up to $8.5 million a year.

In order to improve beach users’ experience, moving forward, an issue like marine debris should be prioritized. Marine debris can be a stressor that impacts coastal tourism worldwide. An evaluation of economic impacts caused by litter presence is a unique approach to analyzing how to minimize the threat litter may pose to tourism revenue. Some factors that may influence a visitor’s beach choice may include beach length, scenery, water quality, amenities (restaurants, shops, etc.), and quantity of litter. The additive effect of these factors determines the overall impression the trip will leave on the visitor. Stranded beach litter is considered to be one of the five most important aspects regarding beach quality in Europe, USA, Mexico, and the Caribbean (Krelling, Williams, & Turra, 2017). More research should be done in order for authorities to decide how to best go about balancing investments to remove marine litter and minimize the potential reduction of tourism revenue. Through integrated planning, the sources of litter can be determined and preventive strategies can be put into play. This would help to avoid a reduction in environmental quality and income generated from tourism.

Works Cited

Krelling, A. P., Williams, A. T., & Turra, A. (2017, August 15). Differences in perception and reaction of tourist groups to beach marine debris that can influence a loss of tourism revenue in coastal areas. (H. Smith, Ed.) Marine Policy.

Millennium Ecosystem Assessment. (2005). Ecosystems and Human Well-being: Synthesis. Washington, DC: Island Press.

Oregon Coast STEM Hub. (2017). Marine Debris – Composition and Abundance. (L. C. Schools, O. C. Newport, N. M. Program, & S. G. (Oregon), Producers) Retrieved from Conserve Wildlife New Jersey:
http://oregoncoaststem.oregonstate.edu/marine-debris-steamss/md-grades-4-5/composition-and-abundance

USFWS – Pacific Region. (2012, January 11). Dr. Sylvia Earle talks to an albatross nesting among marine debris. (A. Collins, Producer) Retrieved from Wikimedia Commons: https://commons.wikimedia.org/wiki/ File:Dr._Sylvia_Earle_talks_to_an_albatross_nesting_among_marine_debris.jpg

Investigating Atlantic Salmon Dive Behavior in the Norwegian and Barents Seas

By Grant Voirol, SRC Intern

Atlantic salmon, Salmo salar, are both an economically and ecologically important organism. An anadromous fish, Atlantic salmon spend most of their lives at sea before swimming into freshwater rivers to spawn. While at sea, Atlantic salmon periodically migrate to depths deeper than 10 meters. One proposed model of their diving behavior is that the salmon dive to deeper colder waters to feed before returning to shallower warmer water to digest. In this way, they can maximize their energy conservation (Reddin et al 2004). However, in colder waters of the most northern Atlantic, temperatures of shallower water are not significantly warmer than the depths that salmon can reach. So what factors govern Atlantic salmon diving behavior in these colder waters?

Picture 1

Atlantic salmon are both popular sport fish throughout the Atlantic as well as important predators and prey. Photo: Hans-Petter Fjeld (CC-BY-SA).

A recent study sought to find out. To do so, researchers studied post-spawning Atlantic salmon in the Norwegian and Barents Seas over season and daily timescales. Three populations from the three rivers Orkla, Alta, and Neiden, were caught and tagged using pop-up satellite archival tags (PSATs) and data storage tags (DSTs). PSATs measure temperature and depth and are attached externally to the salmon. They release themselves from the fish if a predetermined period of days goes by, the fish dives to a depth that will harm the tag (1200 meters), or the tag registers a constant depth, usually meaning the fish has died. Once they release themselves, the tags send a signal to satellites where the data collected as well as its position can be downloaded. DSTs are inserted internally in the salmon and measure temperature and depth at a much higher resolution. However, since the tags are inserted into the salmon, these salmon must be recaptured in order to retrieve the data. Recapture was dependent on fishers who would receive a reward for returning the tags to the researchers.

The findings show that the three groups of salmon displayed similar patterns of dive behavior during the sampled period. On the seasonal time scale, salmon went to deeper depths during winter and spring following the depth of the mixed layer (Figure 1). On daily timescales, the salmon occupied greater depths during daylight hours and returned to nearer to the surface during nighttime hours (Hedger et al. 2017).

Figure 1

Median dive depth per month. Solid line shows depth of the mixed layer. Increases in dive depth occur during the months of November to May. (Hedger et al. 2017)

A better understanding of the distribution and behavior of different populations of Atlantic salmon is important in order to know if different management practices need to be employed in different areas. Furthermore, this information gives us a better picture of the role that Atlantic salmon play in the Northeast Atlantic as both a predator and prey species.

Works Cited

Hedger RD, Rikardsen AH, Strøm JF, Righton DA, Thorstad EB, Næsje TF (2017) Diving behaviour of Atlantic salmon at sea: effects of light regimes and temperature stratification. Mar Ecol Prog Ser 574:127-140.

Reddin DG, Friedland KD, Downton P, Dempson JB, Mullins CC (2004) Thermal habitat experienced by Atlantic salmon (Salmo salar L.) kelts in coastal Newfoundland waters. Fish Oceanogr 13: 24−35.

A comparative analysis of the behavioral response to fishing boats in two albatross species

By Andriana Fragola, SRC Intern

This paper examines the behavior of the Wandering Albatross (WA) and Black-Browed Albatross (BBA), and how they are affected by the toothfish longline fleet in Kerguelen and Crozet (Collet et al. 2017). To do this, lightweight GPS loggers were attached to adult albatrosses of both species to track their movements. To track the fishing boats, VMS data was provided to the researchers which allowed them to log their movements (Collet et al. 2017).

Calculations were done to establish the maximal distance that birds were seen flying towards the fishing boats. To isolate the different behaviors of the albatross the researchers established “encounter” as well as “attendance” behaviors to assess the responses of the birds to these fishing vessels (Collet et al. 2017). Encounters were defined as more by chance when the birds were in flight, while attendance behavior was defined as sitting in the water within a close range of the vessels (Collet et al. 2017).

Figure 1

[Source: Collet et al. 2017]

Results demonstrated that the Black-Browed Albatross (BBA) did not come into contact with fishing vessels as often as the Wandering Albatross (WA) (Collet et al. 2017). BBA also seemed to forage in areas that were a greater distance from the fishing vessels than WA (Collet et al. 2017). When the vessels were absent, BBA were not seen foraging in the regions where the vessels typically operate, while WA were (Collet et al. 2017).

Although WA are the larger and more dominant species, they were not observed pursuing the fishing vessels as much as the researchers had expected (Collet et al. 2017). BBA had an 80% chance of being attracted to fishing vessels, while WA had a lesser 60% chance of being attracted to the boats (Collet et al. 2017).

There were apparent differences between these two species and their utilization of fishing fleets as a means for foraging (Collet et al. 2017). This paper suggests that the energetic needs of each species can be an indicator of the risks associated with foraging from anthropogenic sources (Collet et al. 2017).

Figure 2

[Source: Collet et al. 2017]

It is vital to understand how species are becoming reliant on anthropogenic sources for food because this can affect their nutritional health. The quality of the fish that albatross are getting from these fishing vessels may not have the nutritional value of the fish they typically hunt. Further, if generations of these animals become dependent on these unnatural food sources, this can lead to issues – if the availability of that source becomes compromised, and birds are reliant to the extent that they do not have the skill to forage on their own.

Work Cited

Collet, J., Patrick, S. C., & Weimerskirch, H. (2017). A comparative analysis of the behavioral response to fishing boats in two albatross species. Behavioral Ecology, 28(5), 1337-1347.