Dive Dry with Dr. Bill

#396: See... Sea Lice

It's that time of year when the gentle giants start gathering in the waters off Catalina and other locations in southern California. No, I'm not referring to the gray whale migration seen twice a year along our coast. These giants are a bit smaller, no more than 800 pounds historically. Of course the ones I encounter today are more likely less than half that weight, with a few approaching 600 pounds like the individual the SCICo boat crews named "Dr. Bill." I'm not sure if that was a slight to me, or to the gentle giant.

Yes, I'm referring to the giant sea bass. Although formerly called black sea bass, the American Fisheries Society abandoned that common name in 1961 because it was already in use for an unrelated species on the East Coast. Back in the late 1800s, when they were targeted by both commercial and recreational anglers, they were called jewfish. Fortunately that name was wisely dropped in the 20th century. Unfortunately the anglers were so successful in harvesting this species, they were largely absent from our waters by the time I arrived in the late 1960s. In fact, I didn't see my first one until the late 1990s. Now I have frequent encounters with them each summer. You can even watch them being hand fed by the guys down at Joe's Rent-A-Boat on the Pleasure Pier.

My column today won't focus on the gentle giants themselves. Instead, I want to look at the little "Davids" that attack these great goliaths. I'm referring to the parasitic copepods that one almost always sees covering their body. For years I tried to get the scientific name for these small parasites known as copepods or sea lice, but no one seemed to know. A few years ago, Dr. Milton Love, former Cousteau associate in the 70s and the very fishy ichthyologist at UCSB, suggested to me that these parasites belonged either to the genus Lepeophtheirus or Caligus. While researching the narration for a revised version of my Gentle Giants DVD, I was surprised to find that years ago Hobson identified the parasite on the giant sea bass as Lepeophtheirus longipes.

The life history of these copepods is pretty interesting. During their early stages they drift with the plankton and are not parasitic. Initially as larvae, they do not feed and are sustained by the yolk sac. Later larval stages will attach to fish, but generally do little damage to them. When they mature and settle, they begin their truly parasitic stage by attaching to their victims. Different species of these copepods may choose different host species of fish, but some will parasitize several different fish. Although small in size, copepods make up the greatest proportion of the animal biomass in the world. If we continue harvesting the ocean the way we have, they may become our primary food source.

I'm sure my angler friends have seen parasitic copepods related to these on other fish species they've caught in our waters. Like the ones on the giant sea bass, these usually feed on the tissues, fluids or blood of their host and therefore can weaken their victim when infestations get too great. Salmon farming in fish pens has become an environmental issue over the past decade. The high density due to the concentration of captive fish in the pens has made it much easier for sea lice found on salmon to reproduce more effectively. Free-swimming salmon passing near these pens become infected by the sea lice, thus affecting the wild stocks of fish. Alaska has banned salmon farming for this and other reasons. Of course this can happen when any fish species is raised in high numbers in pens.

When our giant sea bass gather this time of year to spawn, they create the same kind of conditions. Up to several dozen individuals may congregate in close quarters at historical spawning sites. This makes it easy for the sea lice to transfer from one to the other and infect fish which are relatively free of them. The sea lice seen on our gentle giants are often present in large numbers. They could weaken the giant sea bass by removing too much tissue, bodily fluids or blood from individuals. This could have negative impacts on their ability to reproduce.

Fortunately other fish see the sea lice's presence as an opportunity. I'm referring to "parasite pickers" or cleaner fish. I have personally seen young sheephead, senorita, rock wrasse and kelp bass actively picking sea lice off the bodies of the giant sea bass. Cathy deWet Oleson and her husband Jim noted that the small island kelpfish would clean them at specified cleaning stations near reefs off Anacapa Island. Later they saw juvenile giant kelpfish and blue banded gobies do so, along with the species of cleaners I've observed.

Almost all the giant sea bass I observe have their heaviest parasite burden near their heads. When I first observed this a decade ago, I thought the sea lice might be holding on to the bass and freeloading, feeding on scraps of food discarded by the bass. Dr. Love assured me they were indeed true parasites although they freely move around on the body of the fish. Then I observed these parasitic copepods fleeing whenever a cleaner fish would lunge towards them. "Parasite pickers" like sheephead and senorita aren't stupid. They know to keep away from the sea bass' head and its huge mouth that can suck food in. The cleaners focus their efforts everywhere but the head, which is why the sea lice are densest there.

One of the fundamental concepts of ecological systems is the food chain. No, I'm not referring to Vons (or even Trader Joes or Whole Foods). I'm referring to one species munching on another. It's the way the world goes 'round in "the Mutual Eating Society." Plankton are eaten by baitfish which are then consumed by predators like kelp bass which may be munched on by a successful angler who falls out of his boat and is eaten by a great white shark. Just teasing about that last part! Imagine this interesting food chain: sea lice feeds on the tissues and fluids of a giant sea bass, then gets eaten by a sheephead cleaner which is sucked into the the same sea bass' mouth. That's one way of recovering a return on your initial investment!

© 2010 Dr. Bill Bushing. Watch the "Dive Dry with Dr. Bill" underwater videos on Catalina Cable TV channel 49, 10:00 AM and 5:00 PM weekdays and on Charter Communications Cable channel 33 at 7:30 PM on Tuesdays in the Riverside/Norco area. Please help me climb out of self-imposed poverty... buy my DVD's (see this link). Yes, take Dr. Bill home with you... we'll both be glad you did!

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Parasitic copepods infesting head region of giant sea bass, male and female (with white strings of eggs
trailing behind) parasitic copepods; kelp bass and sheephead cleaning parasites from underside of bass,
too close for comfort!

This document maintained by Dr. Bill Bushing.
Material and images © 2010 Star Thrower Educational Multimedia