A simple tool to predict bycatch in harbour porpoises

By Emily Nelson, SRC master’s student

Harbour porpoise bycatch has been identified as the biggest threat facing these animals in many areas today, with many incidental catches occurring in large commercial gillnet fisheries. In efforts to minimize negative impacts, harbour porpoises in waters of the European Union have been awarded protection under Habitats Directive (EC 1992) and Council Regulation 812/2004 (EC 2004). Despite differences in specifics, these policies both work towards conservation and would benefit from increased information regarding bycatch of porpoises.

Harbour porpoise in Denmark. Photo by Erik Christensen.

Harbour porpoise in Denmark. Photo by Erik Christensen.

Kindt-Larsen et al. 2016 aims to create a model that can identify areas and seasons where porpoises are at high risk of entanglement in commercial fishing gear. Two main high-resolution datasets were used to develop the model. First, fisheries and bycatch data was obtained from remote electronic monitoring systems aboard 4 commercial gillnet operations in the Danish part of the Skagerrak Sea. Using video footage of gillnet hauls the authors were able to identify time and location of harbour porpoise bycatch events. Fishing effort (defined as the product of gillnet string length and net soak time), fishing target species (cod, plaice, and hake), and season (winter, spring, summer, and autumn) were also used. Second, estimated population density of harbour porpoises was obtained using satellite tag data from 66 individuals in the same area. Data was filtered to remove positions that may be inaccurate, such as locations that required excessively high swim speed to reach. Further, tag data was manipulated according to a grid system. A value was assigned to each 1km grid cell within the study area reflecting the likelihood the particular cell was visited by harbour porpoises.

Density of harbour porpoises, estimated from satellite tagging data using a grid system.

Density of harbour porpoises, estimated from satellite tagging data using a grid system.

This data was then used to identify the general relationship between expected bycatch and porpoise density. The authors started with the most complex model (involving all variables) and sequentially removed insignificant variables in order to find the best fit. In the end, target species and length of net did not improve the model fit. Additionally, porpoise density estimated using season and area (rather than satellite tag data) did not improve fit. The best model was very simple; harbour porpoise bycatch was best explained using solely soak time of fishing gear and satellite tag estimates of population density.

The success of the model developed by Kindt-Larsen and colleagues relies on a few large assumptions. First, the assumptions that satellite tagged porpoises are representative of the population as a whole. This concern was addressed in a number of ways. 1. Analysis was run showing that the spatial patterns observed were consistent over time. 2. Areas of high density predicted by satellite data were verified because acoustic surveys show similar results. 3.The satellite tagged individuals contained a mixture of juvenile, adult, male and females, thus there is no bias in the data do the demographic differences. The second assumption is that fishing effort estimations are truly representative of the four fisheries. This is verified because fishing effort was calculated the same way throughout all vessels. Lastly, the assumption that recorded porpoise bycatch was representative of the true number of bycaught animals. This assumption was of little concern to the authors because the REM video was of high quality and bycatch was easy to identify. However, if porpoises fell from the net prior to reaching the surface they were not recorded. For this reason it is important to consider bycatch estimates presented here as a minimum. Overall, it seems the assumptions of the model will have minimal impact on results.

The model created by Kindt-Larsen and colleagues follows the simple principle, that bycatch can occur only if the animal and fishery have an overlap in space and time. While the model presented is basic, it can absolutely act as a starting point for investigations of harbour porpoise bycatch. Results will be able to identify regions and/or seasons of high and low risk to porpoises. This will aid in future bycatch monitoring and the development of mitigation strategies.

Works cited

EC (European Commission) (1992) Habitats Directive: Council Directive 92/43/EEC of 21 May 1992 on the conservation of natural habitats and of wild fauna and flora. Off J Eur Union L 206: 7−50

EC (2004) Council Regulation (EC) No. 812/2004 of 26 April 2004 laying down measures concerning incidental catches of cetaceans in fisheries and amending Regulation (EC) No. 88/98. Off J Eur Union L 150: 12−31

Kindt-Larsen, L., Berg, C.W., Tougaard, J., Sorenson, T.K., Geitner, K., Northridge, S., Sveegaard, S., & Larsen, F. (2016). Identification of high-risk areas for harbour porpoise Phocoena phocoena bycatch using remote electronic monitoring and satellite telemetry data. Marine Ecology Progress Series, 555, 261-271.

The response of sandy beach meiofauna to nutrients from sea turtle eggs

By Abby Tinari, SRC intern

South African scientists, Diane et. al (2017), studied how organic matter is transferred through the food web and how this influences consumer populations. Specifically, they chose to look at the interaction between sea turtle eggs and meiofauna in sandy beaches where organic matter is limited.

Loggerhead turtle, species who provided the turtle eggs. (Photo from Wikipedia Commons)

Loggerhead turtle, species who provided the turtle eggs. (Photo from Wikipedia Commons)

Meiofauna are small invertebrates that live in both marine and fresh water environments. The main taxa present in the study were nematodes, insect larvae, collembola, and halacarid. Sandy beaches lack an abundance of organic matter. Diane et. al predicted that the seasonal influx of turtle eggs would generate an increase in meiofauna abundance. To test this, they chose to look at how the meiofauna abundance differs between naturally predated nests and the sand around it as well as how quickly the meiofauna utilized the resource pulse.

The abundance study, looking at the differences in meiofauna population between the preyed upon sea turtle nests and the surrounding sand, sampled 15 nests taking three samples at 5, 20, and 40-centimeter depth from each nest. This was also done for the surrounding sand 2 meters from each of the selected nests to act as the control. These nests were naturally predated on by honey badgers and ghost crabs among other predators. 50 turtle eggs were taken from active nests and placed into 10 pseudo-nests (baskets) for the temporal study. The eggs were cracked to simulate natural predation. Diane et al. took samples at three depths (5, 20 and 40cm) in each the control and the experimental baskets. Samples were taken every day for 20 days. In each experiment the meiofauna was sorted into major taxonomic groups and the density of individuals was counted.

Mean abundances (±SE) of major meiofauna taxonomic groups in the experiment baskets (with turtle eggs: left panel) and control baskets (without turtle eggs: right panel) over the sampling period for the in-situ experiment.(a-b nematodes; c-d halacarid mites; e-f insect larvae; g-h collembolan; i-j unknown 1) (Diane et al. 2017)

Mean abundances (±SE) of major meiofauna taxonomic groups in the experiment baskets (with turtle eggs: left panel) and control baskets (without turtle eggs: right panel) over the sampling period for the in-situ experiment.(a-b nematodes; c-d halacarid mites; e-f insect larvae; g-h collembolan; i-j unknown 1) (Diane et al. 2017)

Diane et al. found that the meiofaunal and nematode abundances were significantly different between the experimental and control nests for both the abundance and temporal study. Nematodes were the dominant taxa in both studies. In the first experiment, for abundance, the meiofaunal diversity was higher in the naturally predated nests than in the control nests around them. Collembolans were the second most dominant taxa in the predated nests while in the control nests insect larvae was the second most abundant taxa. The abundance of most meiofauna decreased with depth except for the collembolans which had similar abundances at the shallowest and deepest depths. In the temporal study the species richness was higher in the experimental baskets than in the control baskets. Diane et al. also found a significant difference in abundance at the middle and bottom depths. Most meiofauna were in the deepest samples close to the eggs. Abundances and maximums varied with time. Nematodes were the first to arrive and die out, followed by insect larvae, halacarid mites and collembolans.

Studying the interactions between trophic levels is useful to know, even on a macroscopic scale. Some of the meiofauna observed were insect larvae that will become consumers and prey for other taxa. Diane mentions that nematodes feed on bacteria and other macrofauna and this could be linked to higher trophic levels. The sea turtle eggs bring a predictable annual source of nutrients that allow the meiofauna to thrive. Other spawning events may have a similar increase in meiofauna populations and abundances with the pulse of organic matter they bring. Knowing the interactions between trophic levels can help scientists better understand the effects of an abundance shift in one of the levels.

Works cited

Diane Z.M., et Le Gouvello, Ronel Nel, Linda R. Harris, Karien Bezuidenhout. 2017. The response of sandy beach meiofauna to nutrients from sea turtle eggs. Journal of Experimental Marine Biology and Ecology 487:94-105.

Finding Nemo’s Anemone

By Leila AtallahBenson, SRC master’s student

A Nemo lookalike in close proximity to an anemone host. [Wikimedia Commons]

A Nemo lookalike in close proximity to an anemone host. [Wikimedia Commons]

Do you remember in Finding Nemo when the eagle ray professor asks the kids where they live, and nemo replies, with some difficulty, that he lives in an anemone? Have you ever wondered about the relationship between the clownfish and their anemone homes? It is known that these two species interact and have a mutualistic relationship. Anemones house and protect clownfish, but what do clownfish do for the anemone? Well, a group of researchers from Boston University took a deeper look at the association of clownfish and anemones.

They conducted a one-and-a-half-year study, where they placed 0, 1, or 2 clownfish in a tank with an anemone. They watched the fish personalities over the course of the study. Fish personalities were described by how much time a fish spent near their anemone home: were they a shy fish, like Nemo’s dad Marlin, and spent most of their time in or around their anemone? Or were they a more outgoing fish, like Nemo, and adventured away from their anemone? They then recorded what growth effects these different personalities had on the anemones.

Predicted anemone growth given the shyness of a fish over the year-and-a-half study. Maximum shyness of a fish is 1200 sec. [Schmiege et al. 2017]

Predicted anemone growth given the shyness of a fish over the year-and-a-half study. Maximum shyness of a fish is 1200 sec. [Schmiege et al. 2017]

As it turns out, shyer fish help anemones show more growth. Anemones with fish residents that spent more time near to them grew significantly more than anemones whose fishy friends spent more time adventuring away from their homes. The scientists proposed that this relationship is seen between shy fish and anemone growth because shy fish provide more oxygenation, nutrients, and freedom to stretch the anemone’s tentacles and feed for themselves. Shy fish swim and move around the anemone more frequently, bringing oxygen to the anemone. Given shy fishes’ increased presence, there is also more fish waste for the anemone to absorb nutrients from. Shy fish are also around to defend their hosts more, which allows the anemone to stretch out its tentacles and absorb more nutrients from the water column. Maybe that’s why Nemo and Marlin’s anemone was the same size when they came back from their adventure, it did not have its shy, fishy friends to help it grow.

An anemonefish next to an anemone, Entacmaea quadricolor, the kind used in the study. [Wikimedia Commons]

An anemonefish next to an anemone, Entacmaea quadricolor, the kind used in the study. [Wikimedia Commons]

Works cited
Schmiege, P.F.P., D’Aloia, C.C., Buston, P.M. 2017. Anemonefish personalities influence the strength of mutualistic interactions with host sea anemones. Marine Biology 164:24.

Atypical and Estuarine Habitat of the Maroni River Mouth Altering Green Turtle Behavior in French Guiana

By Casey Dresbach, SRC intern

Green Sea Turtle, Chelonia mydas. (Your Shot National Geographic, 2013) http://yourshot.nationalgeographic.com/photos/2387735/?source=gallery)

Green Sea Turtle, Chelonia mydas.
(Your Shot National Geographic, 2013) http://yourshot.nationalgeographic.com/photos/2387735/?source=gallery)

 

In this experiment, satellite telemetry was used to assess the behavioral adjustments of twenty-six adult female green turtles. Sixteen Argos-linked Fastloc GPS tags were deployed on green turtles from February to June 2012 on both sides of the Maroni River: Awale-Yalimpo and in the Galibi Nature Reserve in Suriname. At the same time, ten other females in the Amana Nature Reserve were equipped with Conductivity-Temperature-Depth-Fluorometer Satellite Relayed Data Loggers, which provided the locations of the turtles via Argos data, and recorded profiles of the dive depth, time at depth, dive duration and post-dive surface interval, and oceanographic data in the form of vertical temperature and salinity profiles taken during the rising phase of these turtles’ dives as seen in Figures 1 and 2. The intent of tagging was to analyze three entities: home range, diving behavior, and environmental conditions.

Figure 1. Extreme temperatures recorded in-situ by the Argos-Linked Fastloc GPS tags on green turtles Chelonia mydas of 2012.) (Chambault, et al.)

Figure 1. Extreme temperatures recorded in-situ by the Argos-Linked Fastloc GPS tags on green turtles Chelonia mydas of 2012. (Chambault, et al.)

Temperature-salinity diagram for the green turtles tagged with a CTD-SRDL tag in 2014. (Chambault, et al.)

Temperature-salinity diagram for the green turtles tagged with a CTD-SRDL tag in 2014. (Chambault, et al.)

In relation to home range, the findings show that Chelonia mydas stayed close to both the shore and their nesting beach, exhibiting limited movement. By staying close to shore, the turtles are likely to save energy for oviposition, the act of laying their eggs. Regarding diving behavior, dive data showed that individual female green turtles were spending extended periods at the surface. This may be related to their highly diurnal resting activity, where they are active during the day. The data also shows that these turtles went for short and shallow dives. One of the reasons for this suggests basking at the surface, which can be beneficial for thermoregulation, especially in these warmer waters. Also, this behavior permits the avoidance of aggressive males or potential predators, delay of algal or fungal infestations, and also an enhancement of immune response. Additionally, spending time at the surface is associated with both their lungs’ positive buoyancies (being denser than water surrounding it) as well as foraging activity. In terms of finding food, a green turtle’s preferred choice of sustenance is seagrass. However, the waters of the French Guiana provide an extreme environment for these turtles, where large river outputs generate very warm water (~27 to 29° C) and highly variable salinities (1.2 to 35.5 psu), as shown in Figures 1 and 2. In these waters, the high river outflow lead to low levels of irradiance, probably resulting in the lack of seagrass. The turtles of the French Guiana have adapted to this consequence by seeking alternate food sources and also relying on stored body fat for energy, defining the population as capital breeders. Adaptations are often compromises; each organism must do many different things to compensate for their surroundings (Reece, Urry, Cain, Wasserman, & Minorsky, 2014). We humans owe much of our versatility to our flexible limbs, but they are also prone to sprains, torn ligaments, and dislocations. Hence, structural reinforcement has been compromised for agility. These turtles are compromising their preferred food choice because it is unavailable. Their available alternatives include those befitting the water’s turbid environment such as: crustaceans, polychaete worms, and cnidarians. Jellyfish are fairly abundant on the French Guiana continental shelf, and these female turtles are adapting an appetite for an alternative source of nutrition to enable survival.

This study provides the first data to describe the inter-nesting events, habitat use, dispersal and diving behavior of green sea turtles. The findings show this population of Chelonia mydas has adapted many behaviors in response to the deviant and estuarine habitat of the Maroni river mouth. This is the first study to track this specific population of green turtles during their inter-nesting season. Satellite tracking made it possible to locate and quantify the habitat used by Chelonia mydas during their inter-nesting seasons. Their survival is at risk, both with increasing climate change and the life-threatening illegal fishing along the Guiana coast. By evaluating their home range, it makes it possible to obtain a reliable visual of areas where these turtles nest, to thus identify hotspots that need protection. The endangered species is particularly vulnerable during their inter-nesting periods, especially in the atypical environment they are residing in. Further research should be done to evaluate the interactions between green turtles and fisheries to ultimately seek permission to delineate a Marine Protected Area.

Works cited

Chambault, P., Thoisy, B. d., Kelle, L., Berzins, R., Bonola, M., Delvaux, H., et al. (2016). Inter-nesting behavioural adjustments of green turtles to an estuarine havitat in French Guiana. Marine Ecology Progress Series , 555: 235-248 .

Dunand, A. (2013, October 15). Your Shot National Geographic .

Reece, J. B., Urry, L. A., Cain, M. L., Wasserman, S. A., & Minorsky, P. V. (2014). Campbell Biology . Boston: Pearson.

Nocturnal migration reduces exposure to micropredation in a coral reef fish

By Josh Ratay, SRC intern

The French grunt was used as the organism of study, though gnathiid isopods feed on many different species of reef fish. Image from Wikimedia Commons.

The French grunt was used as the organism of study, though gnathiid isopods feed on many different species of reef fish. Image from Wikimedia Commons.

 

Nocturnal migration reduces exposure to micropredation in a coral reef fish is a new study examining daily migrations of French grunt (Haemulon flavolineatum) and the exposure to parasitic isopods. French grunts are known to move off the reefs and into seagrass beds at night. Such behavior in animals is usually attributed to increased availability of prey or decreased exposure to predators. However, this study investigates the idea that the fish’s movements may serve as a method of avoiding isopods, which are far more common on the reefs than in seagrass communities.

The French grunt served as an ideal model organism for this study since it is both extremely common and well-studied on Caribbean reefs. However, many other reef fish are known to undertake similar nightly migrations away from the reef. Gnathiid isopods are tiny parasitic crustaceans which attach to fish and feed on blood. Though they usually hide in reef sediments, the larvae emerge to find a short-term host fish directly before molting and growth. Though far smaller than their hosts, these parasites can have many negative health impacts on fish, including decreased concentrations of red blood cells, tissue damage and infection, and even the death of juvenile fish which are exposed to a high isopod load.

Larval gnathiid isopods (bottom right) feed on the blood of fish before molting. Adult males (left) and females (right) tend to remain in the sediment. Image from Wikimedia Commons.

Larval gnathiid isopods (bottom right) feed on the blood of fish before molting. Adult males (left) and females (right) tend to remain in the sediment. Image from Wikimedia Commons.

In this study, several tests were performed at different locations in the Caribbean to test the hypothesis that leaving the reef at night results in fewer numbers of isopods infesting French grunts. Cages containing 5 to 8 fish were deployed overnight at both reefs and nearby seagrass habitats where grunts had been observed. Also, the exact arrival times (around dawn) of the wild grunts to the reefs were observed at different sites, and cages of grunts were subsequently placed at the reefs for both the 30 minutes preceding the arrival time and 30 minutes following the arrival time. The goal of this test was to investigate whether or not the fish’s arrival time coincided with lessened isopod activity. Additional cages were also deployed to test day versus night isopod levels, and the whether or not juvenile grunts were also susceptible to isopod infestation. All fish from the cages were placed in seawater tanks, where the isopods naturally detached and were then counted.

Box and whisker plot showing the decrease in isopods in the time after the fish have returned to the reef vs. immediately before. Figure from Sikkel et al 2017.

Box and whisker plot showing the decrease in isopods in the time after the fish have returned to the reef vs. immediately before. Figure from Sikkel et al 2017.

Statistical analysis of the data revealed that grunts which spent the night on the reefs contracted 3 to 44 times as many isopods as those which were left in the seagrass bed. Fish which were placed on the reefs during the 30 minutes before the return time of the wild grunts contained twice as many isopods as those which were exposed to the reef after the return time. Nighttime isopod load on the reefs was also much higher than the daytime load, and isopods were detected on juveniles from the reefs but not the seagrass beds. Overall, these results were significant and suggest that moving to seagrass beds at night is an effective method of isopod evasion for both adult and juvenile grunts, and that the fish return in the morning as isopods become less active. The results from this study suggest that further research is needed into the potential for parasites to drive movements of coral reef organisms.

Works cited
Sikkel, P. C., Welicky, R. L., Artim, J. M., McCammon, A. M., Sellers, J. C., Coile, A. M., & Jenkins, W. G. (2016). Nocturnal migration reduces exposure to micropredation in a coral reef fish. Bulletin of Marine Science.

The imperiled fish fauna in the Nicaragua Canal Zone

By Nicole Suren, SRC intern

Plans for a new canal through the isthmus of Nicaragua have just been approved by the Nicaraguan government with little to no restrictions on what preexisting waterways can be used as part of this potential new shipping route. The currently proposed route was planned based on economic and technical considerations, but ecological concerns were not factored into the planning, leading to a variety of potential ecological problems due to the construction of the canal. These ecological detriments include overexploitation of the environment, increased water pollution, water flow modification, destruction or degradation of habitat, and the establishment and spread of non-native species. The currently proposed route is of special concern because it not only passes through Lake Nicaragua, a freshwater ecosystem of very high socioeconomic importance, but also because it connects two currently isolated drainage basins, the San Juan drainage basin and the Punta Gorda drainage basin.

Proposed route (solid line) and alternative routes (dashed lines) of the Nicaragua Canal. The 3 drainage basins involved are San Juan (red), Punta Gorda (blue), and Escondido (yellow). Fish-sampling locations are marked with open diamonds. (Härer et al. 2016)

Proposed route (solid line) and alternative routes (dashed lines) of the Nicaragua Canal. The 3 drainage basins involved are San Juan (red), Punta Gorda (blue), and Escondido (yellow). Fish-sampling locations are marked with open diamonds. (Härer et al. 2016)

This study was conducted in order to establish a baseline of biodiversity in the two potentially affected drainage basins, as well as the surrounding basins, so that changes in biodiversity due to the construction of the new canal can be accurately measured and compared against previous levels. The researchers measured biodiversity by taking surveys of the fish in each ecosystem in question with nets, and then sampling two species each from three families of fish that are common in the area. These samples were then used in a DNA analysis, where common sequences of DNA from each species were analyzed for differences. In general, the more similar the DNA sequences, the more closely connected two populations are, and the less similar the DNA sequences, the less closely connected the populations are. Based on the DNA analysis, “populations within the same basin showed almost no genetic differentiation, whereas comparisons across basins exhibited higher differentiation.” This means that populations of fish within the same drainage basin are very similar to each other, while they are quite different from fish in other, unconnected drainage basins. They also found that Punta Gorda and San Juan have 27 species in common, but they also have 24 and 31 species, respectively, that only occur in one basin.

Diagrams showing connectivity between basins (A-C) and within different locations in the San Juan drainage basin (D-F). The sizes of the circles are proportional to the sample sizes, and the proximity of the circles to each other represent how closely connected they are genetically. (Härer et al. 2016)

Diagrams showing connectivity between basins (A-C) and within different locations in the San Juan drainage basin (D-F). The sizes of the circles are proportional to the sample sizes, and the proximity of the circles to each other represent how closely connected they are genetically. (Härer et al. 2016)

Measures of biodiversity are important because they can be a direct indicator of how healthy an ecosystem is. In other words, a diverse ecosystem is a healthy ecosystem. Since the San Juan and Punta Gorda ecosystems contain populations that are so distinct from one another (which is one of the ways biodiversity is defined), the proposed connection between the two is potentially detrimental to the health of those environments because the physical barriers maintaining their diversity would be removed, thereby reducing their diversity and health. Because of these effects, the authors strongly recommend that the precautionary principle be used, and that a more ecologically sound route for the canal be chosen before starting construction.

Works Cited
Andreas Härer, Julián Torres-Dowdall, Axel Meyer. “The Imperiled Fish Fauna in the Nicaragua Canal Zone.” Conservation Biology, vol. 00, no. 0, 2016, pp. 1-10, doi:DOI: 10.1111/cobi.12768