Residency and long-distance movements of sevengill sharks (Notorhynchus cepedianus) tagged in San Francisco Bay

James T Ketchum,Andrew P Nosal,Michele L Buckhorn,A Peter Klimley,Christina J Slager

doi:10.1186/s40317-017-0141-z

James T Ketchum, Andrew P Nosal + Show 3 more

Open Access

https://doi.org/10.1186/s40317-017-0141-z

Copy DOI

Abstract

BackgroundSevengill sharks are common inhabitants of estuaries and coastal areas and particularly abundant in San Francisco Bay (SFB). There is limited knowledge about the level of residency and migratory movements of this species. We describe the degree of residence of sevengill sharks in SFB and nearby locations, using ultrasonic tags and automated listening stations.ResultsSevengills showed a high degree of residency in SFB, particularly to the Golden Gate (GG) area where they have a strong site preference, both seasonally and inter-annually. Site fidelity was also the highest at the GG. In sharks with deployment times longer than 300 days, we found that > 80% of visits of all mature males were at GG, 80% of visits of a single mature female occurred there, > 85% of visits of most juvenile males, and > 70% of visits of most juvenile females. At GG, sharks moved into the range of the receiver day and night without a strong preference for a particular time of the day, which implies movements up and down the area day and night. At most other locations within the bay, sharks were present during daytime hours, while at Point Reyes during nighttime hours. Sharks moved into SFB during early spring and summer, and moved out of SFB to Point Reyes during late spring and fall. Three sevengill sharks migrated roughly 800 km southeastward along the coastline from SFO, one making three trips back and forth between the sites.ConclusionsThere was strong evidence of residency of sharks within SFB, and sharks repeatedly returned to the same region of the bay with some sharks making long-distance movements.

Highlights

Sevengill sharks are common inhabitants of estuaries and coastal areas and abundant in San Francisco Bay (SFB)
The rates of movement have been described in the San Francisco Bay (SFB) Estuary of downstream migrating late-fall run of the anadromous Chinook salmon [1] and steelhead trout [2]
Adult sevengills are common inhabitants of estuaries and bays from southeastern Alaska to the southern end of the Baja Peninsula, and a population exists within the northern Gulf of California [7]

Summary

Introduction

Sevengill sharks are common inhabitants of estuaries and coastal areas and abundant in San Francisco Bay (SFB). Little is known about the movements and habitat utilization of elasmobranchs within estuaries (e.g., [4, 5]) This is because few Sevengill sharks, Notorhynchus cepedianus, inhabit coastal and shelf waters. This species is common within or adjacent to shallow bays in temperate waters. Adults are commonly captured in Humboldt and San Francisco Bays at certain times of the year, it is not yet known whether they are resident year round and what portion of the population leaves the bays and migrates along the coastal shelf [7].

Methods

Results

Conclusion