Copyright © 2005 Terry Maas, BlueWater Freedivers
 

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BLACK SEABASS RETURN ?

By Terry Maas and Michael Domeier PhD.

"Wow! "This is weird," I thought as I swam shoulder-to-shoulder with a 300-pound black seabass (bsb) on one side and nationally-recognized bsb expert Dr. Michael Domeier Phd. on the other. A half-hour after the sun set over Anacapa Island, I could see just 10 feet through the 60-foot visibility water. The unfamiliar rhythmic sound of my aqualung bubbles punctuated the gathering darkness. Occasionally, lightning flashes brightened the inky water as Mike's strobe blasted the 50 unconcerned gentle giants while they gathered—presumably to breed.

As is the case with other oceanic fishes, we have more questions than answers about the natural history of bsb. Mike, with generous funding from avid angler and spearo Tom Pfleger, has answered many of our basic questions. Later in this article, Dr. Domeier explains his findings after 5 years of intensely studying these wonderful species. While Mike has witnessed captured bsb spawning, he has not yet seen this event in the natural environment. We chose dusk during a brisk current in September—the historical date when the largest aggregations appear—to study the behavior of this particular school. We selected this time because similar species use dusk and currents to allow their fertilized eggs to disburse before local bait fish decimate the spawn.

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Three years ago, local divers shared with me their secret location where they found a large school of bsb. For the next several weeks, while the water remained clear, I freedove with over 50 fish ranging in size from 100- to 300-pounds. Unlike other bsb gathering locations, this reef contains no kelp. Instead of orienting with the kelp as a kind of signpost, these fish swim unfettered over the rocky bottom and often suspended high in the water column. As with other schools of bsb, it is possible to approach to within a few feet of these aquatic Volkswagens as they range over the sand and rock bottom, while they orient their direction into the oncoming current. 

Several years ago, I first met Dr. Domeier at a scientific conference on the monitoring of the newly created Channel Island marine reserves off the coast of California. After I described the gathering of bsb, Mike was eager to observe the school first hand and perhaps, document breeding behavior in the wild.

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Dr. Domeier

Mike and I, equipped with our cameras, dove into the inky post-sunset waters. As the water darkened, the giants came closer, often within reach—but we still observed no overt breeding activity. Mike explained that usually female bsb hydrate their eggs several hours before spawning, making their huge bodies blimp-like. Males develop a pronounced whitish color change at their vent. We were disappointed because we saw none of these changes. Mike had so many questions… Do bsb breed at dusk like the fish in captivity he observed? Do they join in a seething mass like the snapper we both observed in Panama, or do they court like white seabass with several attentive males herding and bumping a single female? Several of my friends who turned me on to this spot observed males discharging what they thought was milt ahead of a female who then swam through the milky cloud. 

Mike agreed that this particular aggregation on Anacapa Island is unique. Many of the aggregations he documented occur in kelp forests and included up to 10 individuals. This particular group of fish contains at least 50 individuals suspended in the water column, from 40- to 80-feet deep, far from the kelp forest that had been decimated earlier this summer by an influx of warm water.

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My roots as a marine biologist are anchored firmly in coral reef fish ecology.  That goes a long way towards explaining my immediate draw to giant sea bass (locally called black seabass in California) when I relocated from south Florida to southern California in 1992.  I noted many parallels between Florida’s situation with goliath grouper and California’s giant sea bass; not only had both species been seriously overfished but both had recently been protected by state law.  I had been involved in goliath grouper research in Florida and was eager to have a look at giant sea bass since they were virtually unstudied at the time. 

Both goliath grouper and giant sea bass get very large, have lifespans about as long as humans and reproduce at a relatively modest rate compared to other fish species.  Furthermore, both species aggregate at specific times of the year, presumably to spawn.  All of the above characteristics make these fishes very vulnerable to overfishing since they can easily be removed quicker than they can reproduce.  Their large size and approachable manor made them an easy trophy for spearfishermen and it is very likely that these are two rare examples where spearfishing had a negative impact on a fish population.  Once an aggregation site was located it could be hammered year after year until the fish were gone. 

The 1990’s saw the advent of some revolutionary types of electronic fish tags that allowed researchers to track and monitor individual fish movements.  Both acoustic tags and satellite popup tags were suddenly responsible for unraveling mysteries about fish that we could never have imagined possible.  Acoustic tags are small pingers that we surgically implant inside the fish so that every time they swim past a data logging hydrophone (an acoustic receiver or “listening station”) the fishes ID is recorded as well as time and date.  Some tags can even transmit swimming depth to the hydrophone.  In 2000 I decided to study giant sea bass by implanting acoustic tags on a number of adult fish and then setting up a large array of hydrophones to track their movements.  

Anacapa Island was chosen as the study site since it was a well known site for catching trophy giant sea bass when they were legal quarry; and an avid scuba diver, Kathy de-Wet Oleson, had recently discovered a good aggregation site.  With generous funding from Tom Pfleger we were able to begin a program that would involve completely surrounding Anacapa Island with hydrophones and surgically implanting  acoustic tags in about twenty giant sea bass.  In early June of 2000 I began the intensive diving that was required to install all the hydrophones on subsurface moorings and then began fishing for giant sea bass.  I conducted the first surgeries in late June and July and by the following June had tagged 21 fish between 80 and 200 pounds. 

Every 3 to 4 months we would go back into the field to dive and retrieve each hydrophone, download the data and change the batteries before putting it back in the water.  We soon learned that these fish behave much differently than Florida’s goliath grouper in that they did not stay in the same place for very long.  While an individual goliath grouper could be found on the same wreck for months on end (I tagged some of these off Key West), giant sea bass were continuously on the move.   I also noticed that the giant sea bass were dropping off my array in the winter.  To figure out where they were going we placed another ring of hydrophones around Anacapa in deeper water; these now required the use of an ROV to retrieve data since they were placed to deep for SCUBA.  We also placed hydrophones around Santa Catalina Island, Santa Barbara Island, Santa Cruz Island and Santa Rosa Island.  We suddenly found ourselves with the largest acoustic tracking array in the world.  In fact, through deploying and maintaining this array I developed many new techniques that led to my writing a methods manual for other scientists who wanted to study fish with acoustic tagging arrays. 

After more than 5 years of data collection with our acoustic array we finally pulled all the gear out of the water in November of 2006.  During that time span we amassed an incredible amount of data; we accumulated over 5 million hydrophone “hits” from the giant sea bass we had tagged and I am just now beginning to analyze the findings.  One very obvious pattern is that these spend the cold winter months in much deeper water; for example, the average swimming depth of one fish was 59.7 feet in August of 2002 but 140.2 feet in December of the same year.  We’ve routinely tracked fish to depths greater than 350 feet in the winter. Also, four individual fish traveled each year from Santa Catalina Island to Anacapa Island to participate in the aggregation before returning to Catalina. Once these fish decided to make the move they traveled the 50 nm distance between these island in just a little over a day (27 hours), swimming across water as deep as 3000 feet. 

Like goliath grouper, giant sea bass have a diet that consists primarily of things they can forage from the sea floor.  Skate, rays, flatfish (flounder, turbot, sand dabs etc.), lobster and mantis shrimp were all commonly found in the stomachs of fish we caught for this study.   Occasionally we would find a barred sand bass or kelp bass, but these were far and few between. 

Although there seems to be anecdotal evidence that giant sea bass are slowly beginning to increase in numbers, they have not responded to their protected status nearly as well as goliath grouper have in Florida.  Goliath grouper have reoccupied much of the inshore waters of Florida and all sizes can be found, from they small juveniles in the Everglades to the big adults on offshore wrecks.  Giant sea bass have been protected even longer than goliath grouper, so why haven’t they responded as well?   Why don’t we see lots of the bright orange juveniles and see adults throughout southern California?  There are good spots for viewing giant sea bass (La Jolla, Catalina Island, Anacapa Island) but they are not found everywhere.  One answer may be the very high loads of PCB and DDT I found in California’s giant sea bass population.  These pollutants are concentrated in the lipid-rich tissues like the brain, liver and ovaries.  Since the eggs are receiving a big dose of these chemicals, they may well be negatively affecting the reproductive success of this species.  It has also been shown that these compounds can act as estrogen mimics in fish, wreaking havoc in males, sometimes causing them to turn into females.   None of the above have been documented in giant sea bass, but at the same time, no one has looked. 

Most underwater hunters have no problem simply enjoying the sight of these big beautiful fish, but it seems the temptation is too much for some.  Sadly, about once a year I am sent a photo of a giant sea bass swimming with a spear shaft either protruding from the body or dragging it behind by the shooting line.  Those of us who know better need to take every opportunity to put pressure on the few who commit such acts to reduce the incidence of unnecessary mortality.

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Copyright © 2006 Terry Maas, BlueWater Freedivers