First Insights Into the Horizontal Movements of Whale Sharks (Rhincodon typus) in the Northern Arabian Sea

Whale sharks off the western coast of India have suffered high levels of fishing pressure in the past, and today continue to be caught in small-scale fisheries as by-catch. Additionally, coastlines in this region host very large and growing human populations that are undergoing rapid development. This exacerbates ongoing anthropogenic threats to this species such as pollution, habitat loss, and ship traffic. For these reasons, there is an urgent need for data on movement patterns of whale sharks in this region of the Indian Ocean. Here, we address this issue by providing the first data on the horizontal movements of whale sharks tagged in the northern Arabian Sea off the western coast of the Indian state of Gujarat. From 2011 to 2017, eight individuals, ranging from 5.4 to 8 m were tagged and monitored using satellite telemetry. Tag retention varied from 1 to 137 days, with the sharks traveling distances of 34 – ∼2,230 km. Six of the eight individuals remained close to their tagging locations, although two sharks displayed wide ranging movements into the Arabian Sea, following frontal zones between water masses of different sea surface temperatures. We explore the relationship between the movement patterns of these whale sharks and the physical and biological processes of the region.

The effects of water temperature, acoustic tag type, size at tagging, and surgeon experience on juvenile Chinook salmon (Oncorhynchus tshawytscha) tag retention and growth

Background Acoustic telemetry is a widely used tool to study the movement and survival of juvenile fish and often requires a surgical procedure to implant the transmitter, which may impact overall fitness and survival following release. This is an important consideration when implementing large-scale acoustic telemetry projects aimed at estimating outmigration survival. The objective of this study was to examine the effects of water temperature, tag type, size at tagging, and surgeon experience on tag retention and growth rate of juvenile Chinook salmon (Oncorhynchus tshawytscha). We tagged 128 spring-run Chinook salmon (81–97 mm fork length, 5.2–10.0 g, tag burden 2.4–6.0%) with one of two types of acoustic transmitters; a shorter, heavier model (‘standard’) and a longer, lighter model (‘injectable’). Fish were tagged by either a novice or experienced surgeon. An additional 64 untagged fish served as a control group and were split between temperature treatments. Fish were reared in either cool (mean 13.4 °C) or warm (mean 17.8 °C) water for 60 days, prior to being euthanized, weighed and measured. Results Tag retention was similar for both transmitter types, but varied with water temperature, with significantly higher tag loss in the warm treatment (21.9%, 14 tags expelled), compared to the cold treatment (7.8%, 5 tags expelled). In the warm treatment, fish growth in the injectable tag group was significantly lower compared to the control group, and lower than the standard tag group, but not significantly lower. There was no significant difference between the control and standard tag groups for the warm treatment. In the cool temperature treatment, fish growth was not significantly different among any of the factors tested. Surgery time differed between surgeons; however, surgeon experience did not significantly affect tag shedding or growth. Conclusion Total tag loss was 14.8% over the 60-day trial, with higher and earlier loss in the warmer treatment. Tag length may be a more important factor than tag weight in smaller size fish. This suggests that tag shedding is a significant factor to consider when estimating survival, as the actual survival rate may be higher than estimates based solely on receiver detections.

From 95 to 59 Millimeters: A New Active Acoustic Tag Size Guideline for Salmon

Two laboratory studies evaluated small Chinook salmon Oncorhynchus tshawytscha (36–99 mm fork length [FL], 0.7–26.7% tag burden) survival, tag retention, and growth (n = 539), and critical swimming speed (Ucrit; n = 241). Fish were implanted with a new active acoustic tag and compared to untagged controls at 12 °C and 17 °C. Across studies no temperature differences were detected. All control fish survived. All tagged fish ≥ 58 mm FL survived and retained their tags. Regression models predicted ≥ 98.6% survival and retention for tagged fish ≥ 58.6 mm FL or ≥ 1.9 g (4.2% tag burden). No growth differences among treatments were identified. Spline regression analysis indicated Ucrit was similar for control and tagged fish that measured ≥ 57.3 mm FL. We recommend tagging salmon ≥ 59 mm FL or ≥ 1.9 g (≤ 4.2% burden), although the guideline should be confirmed in a field setting. Study results represent an important step towards using the new active tag in acoustic telemetry field studies that estimate short-term (30-day) survival of small salmonids.

Escapement of Broodstock Chinook Salmon From Whitlock Bay Spawning Station, Lake Oahe, South Dakota

Feral spawning fall Chinook salmon (Oncorhynchus tshawytscha) in Lake Oahe, South Dakota, are captured using a fish ladder and catch raceway at Whitlock Bay Spawning Station. The number of salmon that escaped the catch raceway and descended the fish ladder prior to spawning was unknown. During October 2017, all salmon that ascended the fish ladder at the spawning station were tagged. Tagged males remained in the catch raceway. Tagged females were moved to other secure raceways and used to estimate tag retention. Of the 383 tagged males, 159 (41.5%) were initially designated as escaped from the catch raceway. Tag loss in the females was 3.9%. Thus, the estimated male salmon escapement rate from the catch raceway was 37.6%. Male salmon remained in the catch raceway for one-to-three days before escaping. The escapement rate decreased over the month-long spawn, with nearly 60% of the males going back down the fish ladder in the first week of October, compared to less than 20% escapement by the final week. Such high rates of escapement from the spawning station may be negatively impacting the spawning efficiencies. Possible solutions include re-engineering of the fish ladder or daily removal of the salmon in the catch raceway to other more secure locations at the spawning station.

Visible implant elastomer (VIE) success in early larval stages of a tropical amphibian species

Animals are often difficult to distinguish at an individual level, and being able to identify individuals can be crucial in ecological or behavioral studies. In response to this challenge, biologists have developed a range of marking (tattoos, brands, toe-clips) and tagging (banding, collars, PIT, VIA, VIE) methods to identify individuals and cohorts. Animals with complex life cycles are notoriously hard to mark because of the distortion or loss of the tag across metamorphosis. In amphibians, few studies have attempted larval tagging and none have been conducted on a tropical species. Here, we present the first successful account of VIE tagging in early larval stages (Gosner stage 25) of the dyeing poison frog (Dendrobates tinctorius) coupled with a novel anesthetic (2-PHE) application for tadpoles that does not require buffering. Mean weight of individuals at time of tagging was 0.12 g, which is the smallest and developmentally youngest anuran larvae tagged to date. We report 81% tag detection over the first month of development, as well as the persistence of tags across metamorphosis in this species. Cumulative tag retention vs tag observation differed by approximately 15% across larval development demonstrating that “lost” tags can be found later in development. Tagging had no effect on tadpole growth rate or survival. Successful application of VIE tags on D. tinctorius tadpoles introduces a new method that can be applied to better understand early life development and dispersal in various tropical species.

Visible implant elastomer (VIE) success in early larval stages of a tropical amphibian species

Animals are often difficult to distinguish at an individual level, but being able to identify individuals can be crucial in ecological or behavioral studies. In response to this challenge, biologists have developed a range of marking (tattoos, brands, toe-clips) and tagging (PIT, VIA, VIE) methods to identify individuals and cohorts. Animals with complex life cycles are notoriously hard to mark because of the distortion or loss of the tag across metamorphosis. In frogs, few studies have attempted larval tagging and none have been conducted on a tropical species. Here, we present the first successful account of VIE tagging in early larval stages (Gosner stage 25) of the dyeing poison frog (Dendrobates tinctorius) coupled with a novel anaesthetic (2-PHE) application for tadpoles that does not require buffering. Mean weight of individuals at time of tagging was 0.12g, which is the smallest and developmentally youngest anuran larvae tagged to date. We report 81% tag detection over the first month of development, as well as the persistence of tags across metamorphosis in this species. Cumulative tag retention versus tag observation differed by approximately 15% across larval development demonstrating that “lost” tags can be found later in development. Tagging had no effect on tadpole growth rate or survival. Successful application of VIE tags on D. tinctorius tadpoles introduces a new method that can be applied to better understand early life development and dispersal in various tropical species.