Survival and Growth of Juvenile Pacific Lampreys Tagged with Passive Integrated Transponders (PIT) in Freshwater and Seawater

Abstract

Tagging methods are needed for both adult and juvenile life stages of Pacific lampreys Lampetra tridentata to better understand their biology and factors contributing to their decline. We developed a safe and efficient technique for tagging juvenile Pacific lampreys with passive integrated transponder (PIT) tags. We tested the short‐term survival of PIT‐tagged juvenile lampreys in freshwater at four temperatures (9, 12, 15, and 18°C) and their long‐term growth and survival in seawater. For both experiments there was little to no tag loss, and juvenile lampreys in freshwater showed high survival at all temperatures at 7 d (95–100%) and 14 d (88–100%) posttagging. Prolonged holding (40 d) resulted in significantly lower survival (28–79%) at warmer temperatures (12–18°C). For juvenile lampreys tagged in freshwater and then transitioned to seawater, survival was 97% for tagged fish until day 94, and at the end of 6 months, survival was about 58% for both tagged and control fish. About half of the tagged and control fish that survived in seawater grew, but there was no difference in growth between the two groups. In freshwater, but not in seawater, most fish that died had an aquatic fungal infection. In both experiments, survival increased with increasing fish length at tagging. Our results indicate that tags similar in size to a 9‐mm PIT tag are a feasible option for tagging metamorphosed juvenile lampreys migrating downstream and that when fungal infections are mitigated—as in seawater—long‐term (at least 6 months) survival of tagged juvenile lampreys is high.

Effects of passive integrated transponder (PIT) implantation on Pacific lamprey ammocoetes

“…Both the stress associated with this transition and changes in organ position may complicate tagging of lamprey that are starting to transform. For example, while we had the greatest success with a lateral incision on Pacific lamprey ammocoetes, other researchers using fully metamorphosed Pacific lamprey have successfully used a ventral incision [12,13]. One of the largest ammocoetes we tagged in late November 2013 successfully metamorphosed by December 2015, indicating that metamorphosis can proceed in lamprey bearing a PIT tag.…”

“…Mesa et al [13] also reported extremely variable growth of transformed Pacific lamprey bearing PIT tags that were held in the laboratory for an extended period. This suggests that, as is the case for many species held in captivity, individual lamprey compete differentially for limited food resources.…”

“…A disinfected 8.4-mm PIT tag (1.4 mm diameter, 0.034 g, Biomark HPT8) was gently inserted into the body cavity, and the incision was not closed with sutures or any other method, as described by Mesa et al [13]. Controls were marked at the same location (approximately 12 mm posterior to gill slits) by injecting a 2-mm streak of uncured yellow VIE (Northwest Marine Technology, Inc.) under the skin (as in [5]).…”

“…Ammocoetes need to move rapidly and burrow successfully to survive. Their anguilliform movements can facilitate tag loss, and their relatively thin skin and lack of scales may contribute to eventual tag extrusion [10,13]. Finally, metamorphosis in lampreys involves profound morphological, physiological, and behavioral changes that must not be interrupted or delayed by the presence of a tag [8].…”

“…A number of studies have used 10-to 12-mm PIT tags to individually mark relatively large (>120 mm) metamorphosed Pacific lamprey Entosphenus tridentatus [11][12][13]. Large (>120 mm) sea lamprey Petromyzon marinus ammocoetes have also been marked with these PIT tags to examine movements and distribution in the field [8].…”