The California market squid, Loligo opalescens, bridges the
subtidal and pelagic (open water) nearshore habitats of the central and southern California coastline. This species is the target of California’s largest and most valuable marine fishery, and because the fishery is conducted on and around the spawning ground, consideration must be given to spawning habitat. Our goal is to inform management by providing agencies with methods and critical data on the reproduction biology of mobile, aggregating squids.
|Figure 1. Typical spawning pod of squids off Cannery Row at thirty-five-meter depth, just beyond the kelp beds. photo Roger Hanlon
Squids play a central role in nearshore marine ecosystems worldwide, not only as the prey of many marine mammals, birds, and fishes but as predators on a wide variety of crustaceans and fishes. Juveniles and adult Loligo opalescens are a key food
component of nineteen fish, nine bird, and two marine mammal species in the nearshore pelagic ecosystem.
The life cycle of squid is very short -- less than one year -- and therefore squid stocks are dependent upon successful reproduction every year. The fishery in Monterey Bay has, for 140 years, centered on the spawning grounds off Pacific Grove and Monterey. Sustainable fishing has been achieved for most of that period, despite the fact that fishing pressure has increased substantially over the past decade. Fishing is now being conducted both during the day, when the squid are spawning, and at night. There is limited protection of spawning grounds through weekend closures. While stocks seem to be healthy, fishery managers continue to ask how best to balance protection of spawning beds with a viable fishery.
It has long been thought that the main mode of reproduction for Loligo opalescens is large-scale spawning events at night followed by mass death. However, recent research has shown that this is not the case in Monterey Bay. Squids spawn most commonly during the day and in small groups (Figure 1) in which egg deposition is slow and immediate die-offs do not occur. Thus, it seems prudent to determine the exact locations of the spawning grounds, and to develop methods to quantify mating and egg laying, to ensure that sufficient eggs are deposited before the squids are harvested.
Using Acoustic Technology to Quantify and Monitor Egg Beds
In 2003 we began testing the notion that acoustic technology could be used to image bundles of gelatinous squid egg capsules called egg mops. Squids are one of the few marine species that deposits its eggs in masses on the seafloor. It was our hope that these egg mops would be amenable to quantification and monitoring.
After testing an array of equipment during recent sea trials in Monterey and the Channel Islands, we found that high-frequency side scan sonar towed about five to ten meters above the bottom was capable of distinguishing egg mops 0.5 meters or greater in diameter. (See Figure 2.) We know from recent ROV trials in Monterey Bay that most eggs are found on open, sandy substrate
in depths of twenty-five to fifty meters.
|Figure 2. Side scan sonar mosaic of a sandy bottom area, 105 by 162 meters, off Pacific Grove, showing squid egg mops in the central region.
By means of side scan sonar samples acquired from a fifty-meter-wide swath extending twenty-five meters on either side
of the towfish, sufficient overlap in adjacent swaths, and GIS
positioning, we have assembled mosaics of side scan sonar images for quantification. Through video photography we have verified distinctive sonar features as being due to egg mops. Given success with the verification in 2004, we will perform larger-scale surveys in Monterey Bay in 2005. We anticipate that a systematic survey comprising ten square kilometers could be completed within five days and that the post-survey analysis could be completed in two weeks. These time scales would make the method practicable as a monitoring tool, so that data accumulated seasonally and yearly could be used to measure potential recruitment.
Using Video and Acoustic Technology to Quantify and Monitor Mating and Egg Laying
Fishermen generally attempt to harvest the squids as soon as they arrive near or at the spawning grounds. Our recent ROV work suggests that the squids require several days (if not longer) of spawning to produce any significant numbers of egg beds. We learned that only small "spawning pods" of squid descend from the large schools in the water column to engage in sexual selection behaviors. (See Figure 1.) It would be beneficial to develop a method that allows monitoring of spawning activity so a judgment could be made about when to allow targeted fishing -- for example, focusing fishing efforts after egg mops are made or when spawning is complete. So the question arises: could we quantify how many squids are actively engaged in benthic spawning?
Standard fathometers used by fishermen can locate squid in the water column, especially when in large aggregations. The video display of such fathometers is not suitable for quantitative work. Scientific echo sounders such as the Simrad EK60/200-kHz system can image both large aggregations and individual organisms. Groups of organisms observed near the bottom at the time of squid spawning appear to be in the size range of squids and are likely to be squids, yet we have to validate these images visually in a fashion similar to our research on squid eggs. This will be the subject of our research beginning in 2005.
By concentrating first on benthic egg mops, we have shown
that acoustic technology can measure reproductive output on the main spawning grounds. We will now apply acoustics to measure the dynamic process of mating and egg-laying, which is possible because this takes place at the bottom, in discrete social groups
in the vicinity of existing communal egg beds.
The eventual goal is to accomplish an ecologically-based (specifically, a behaviorally-based) monitoring and management plan for squids in Monterey Bay. Current fishing pressure mandates such a goal if the squid stock(s) is to be effectively managed. Since the Monterey squid fishery is geographically concentrated, and the fleet relatively small, one can envision real-time, ecology-based management of squids. This may take five to ten years of technology refinement, accumulation of biological information, and close cooperation with fishermen, but the rewards would be substantial for all parties concerned as well as the overall ecological health
of Monterey Bay.
Only space limitations prevent proper acknowledgement of
the historical work that is built upon here and the valuable assistance rendered by many colleagues, most recently by R. Kvitek
and P. Iampietro at California State University Monterey Bay. Support for the work has been provided by the National Undersea Research Center (NURC) West Coast and Polar Regions, National Sea Grant, the Sholley Foundation, and the Packard Foundation.
Roger T. Hanlon1 and Kenneth G. Foote2
1Marine Biological Laboratory, Woods Hole
2Woods Hole Oceanographic Institution