Survival, healing, and swim performance of juvenile migratory sea lamprey (Petromyzon marinus) implanted with a new acoustic microtransmitter designed for small eel-like fishes.

Background: Little is known about the transformer stage of the parasitic lampreys, a brief but critical period that encompasses juvenile out-migration from rivers to lakes or oceans to begin parasitic feeding. Information about this life stage could have significant conservation implications for both imperiled and invasive lampreys. We investigated tag retention, survival, wound healing, and swim performance of newly transformed sea lamprey (Petromyzon marinus) implanted with a new micro-acoustic transmitter, the eel-lamprey acoustic transmitter (ELAT), in a controlled laboratory environment. Results: The 61-day survival of our tagged subjects was 71%, within the range reported in similar studies of juvenile lampreys. However, survival was significantly lower in the tagged animals (vs control), with no effect statistically attributable to measures of animal length, mass, condition, or population of origin (Great Lakes vs. Atlantic drainage). Mortality in tagged fish was concentrated in the first four days post-surgery, suggesting injury from the surgical process. An unusually long recovery time from anesthesia may have contributed to the increased mortality. In a simple burst swim assay, tagged animals swam significantly slower (- 22.5%) than untagged animals, but were not significantly different in endurance swim tests. A composite wound healing score at day four was a significant predictor of maximum burst swim speed at day 20, and wound condition was related to animal mass, but not length, at the time of tagging. Conclusions: Impairments to survival and swim performance of juvenile sea lamprey implanted with the ELAT transmitter were within currently reported ranges for telemetry studies with small, difficult to observe fishes. Our results could be improved with more refined anesthesia and surgical techniques. The ability to track migratory movements of imperiled and pest populations of parasitic lampreys will improve our ability to estimate vital rates that underlie recruitment to the adult population (growth, survival) and to investigate the environmental factors that regulate the timing and rates of movement, in wild populations.

Applications of deep convolutional neural networks to predict length, circumference, and weight from mostly dewatered images of fish.

Simple biometric data of fish aid fishery management tasks such as monitoring the structure of fish populations and regulating recreational harvest. While these data are foundational to fishery research and management, the collection of length and weight data through physical handling of the fish is challenging as it is time consuming for personnel and can be stressful for the fish. Recent advances in imaging technology and machine learning now offer alternatives for capturing biometric data. To investigate the potential of deep convolutional neural networks to predict biometric data, several regressors were trained and evaluated on data stemming from the FishL™ Recognition System and manual measurements of length, girth, and weight. The dataset consisted of 694 fish from 22 different species common to Laurentian Great Lakes. Even with such a diverse dataset and variety of presentations by the fish, the regressors proved to be robust and achieved competitive mean percent errors in the range of 5.5 to 7.6% for length and girth on an evaluation dataset. Potential applications of this work could increase the efficiency and accuracy of routine survey work by fishery professionals and provide a means for longer-term automated collection of fish biometric data.

Diel activity of newly metamorphosed juvenile sea lamprey (Petromyzon marinus).

Timing of activity, especially for juvenile anadromous fishes undertaking long migrations can be critical for survival. River-resident larval sea lamprey metamorphose into juveniles and migrate from their larval stream habitats in fall through spring, but diel timing of this migratory behavior is not well understood. Diel activity was determined for newly metamorphosed sea lamprey using day/night net sampling and passive integrated transponder (PIT) telemetry in two natural streams and PIT telemetry in an artificial stream. Downstream migration was primarily nocturnal in all studies. All but one of 372 sea lamprey were captured during night sampling in the day/night net collections and all detections (N = 56) for the in-stream PIT telemetry occurred within a few hours after sunset. Most (81% of 48) tagged lamprey moved downstream during the first night following release and moved at speeds consistent with observed water velocities. During long-term observation of behavior in the artificial stream most sea lamprey movement occurred during the night with limited occurrence of movement during daylight hours. Understanding seasonal and diel timing of downstream migration behavior may allow more effective management of sea lamprey for both conservation and control.

Push and pull of downstream moving juvenile sea lamprey (Petromyzon marinus) exposed to chemosensory and light cues.

Visual and olfactory stimuli induce behavioural responses in fishes when applied independently, but little is known about how simultaneous exposure influences behaviour, especially in downstream migrating fishes. Here, downstream moving juvenile sea lamprey (Petromyzon marinus) were exposed to light and a conspecific chemosensory alarm cue in a flume and movement were monitored with overhead cameras and nets. When exposed to light, sea lamprey were more likely to be captured in a net closest to the light array. When exposed to the alarm cue, sea lamprey transit rate through the flume increased, but sea lamprey did not avoid the alarm cue plume by moving perpendicular to flow. When the alarm cue and light were applied simultaneously in a push and pull configuration, the alarm cue still triggered enhanced downstream movement (push downstream) and more sea lamprey was still captured in the net nearest the light (pull to the side), resulting in twice as many sea lamprey being captured in the lighted net relative to controls. To our knowledge, this is the first study using multiple sensory cues in a push-pull configuration to modulate fish outmigration. Push and pull of juvenile sea lamprey with sensory cues could be useful to reduce turbine entrainment where native and enhance trap catch where invasive.

A portable trap with electric lead catches up to 75% of an invasive fish species.

A novel system combining a trap and pulsed direct current electricity was able to catch up to 75% of tagged invasive sea lamprey Petromyzon marinus in free-flowing streams. Non-target mortality was rare and impacts to non-target migration were minimal; likely because pulsed direct current only needed to be activated at night (7 hours of each day). The system was completely portable and the annual cost of the trapping system was low ($4,800 U.S. dollars). Use of the technology is poised to substantially advance integrated control of sea lamprey, which threaten a fishery valued at 7 billion U.S. dollars annually, and help restore sea lamprey populations in Europe where they are native, but imperiled. The system may be broadly applicable to controlling invasive fishes and restoring valued fishes worldwide, thus having far reaching effects on ecosystems and societies.