Dive Dry with Dr. Bill

#464: Topsmelt

I've been working on a few new episodes of my cable TV show, one of which focuses on the "baitfish" in our waters. "Baitfish" do not represent a scientific group of related species. They are the schooling fish that are often used by anglers to catch larger, predatory fish such as yellowtail, barracuda or bonita. Oh, and I'm working on that episode ("Predators") as well. The three primary species of baitfish I'm covering are the jack mackerel, the Pacific sardine and the topsmelt. I'll also talk about the northern anchovy and chub or Pacific mackerel, but I just don't have enough footage to really do them justice!

This week I want to take a close look at the topsmelt. Before I do, I would like to mention a new resource I'm using to write these columns and the narration for my cable TV shows. For the past 15 years I've relied on a book by Dr. Milton Love of UCSB. I've known Milton since the mid 1970s when we worked together on Jean-Michel Cousteau's Project Ocean Search programs along with "Her Deepness," Dr. Sylvia Earle. I've recommended this book, Probably More Than You Want to Know About the Fishes of the Pacific Coast, to many people over the years. No more. Milton recently released a new edition he's entitled Certainly More Than You Want to Know About the Fishes of the Pacific Coast. It retains his unique sense of humor and is a magnificent resource even for the lay person interested in our fine finned friends. At a "mere" 650 pages, it is dwarfed by my doctoral dissertation (671 pp), but is far more readable and informative. Buy it.

Topsmelt (Atherinops affinis) are commonly seen in the Casino Point dive park since they frequent shallow nearshore waters close to the surface (rarely below about 75 ft). In addition to being found in kelp forests, one may also encounter them in shallow bays and estuaries. They tolerate a very wide range of salinities and temperatures, making them adaptable to many different habitats. Their geographic range extends from the Queen Charlotte Islands in British Columbia, Canada, down to southern Baja. Fossil records show they've been residents of southern California since the late Miocene (7.6-8.6 million years ago), thus they are indeed "natives.".

These fish reach a maximum length of about 15 inches, about 2 1/2 inches shorter than than their big brother the jacksmelt. Even the largest weigh less than a pound. Not much opportunity for a "fish story" there. They are green to bluish on their back with silver sides and a bright silver stripe edged in blue running the length of the body. The eyes are small. The short, rounded snout has a small mouth at the end with the top lip folded down. The pelvic fins are long relative to the body compared to most fish.

Topsmelt are not true smelt, which are found much further north. They belong to the silversides family, Atherinidae. Other members seen in our waters include the larger jacksmelt and the grunion. These three look very similar with the exception of where the dorsal fins are located. In the jacksmelt, it is forward of the vent or beginning of the anal fin; in the topsmelt it is just above the vent and in the grunion it is behind the vent. You can often tell the difference while observing them in the water. Topsmelt also have forked teeth which distinguishes them from the jacksmelt, but only their dentists can tell.

During the day topsmelt often hide under the kelp canopy, but under cover of darkness they may go out in open water. Although they mostly live and feed near the surface, there are reports of the larger ones rooting along shallow bottoms. Juveniles feed on plant plankton, algae and kelp fly larvae (yummy). Adults add small crustaceans, worms, the exposed siphons of clams, fish eggs and small fish to their menu. What goes up must go down, and what eats must get eaten. Topsmelt predators include bony fish (California halibut, kelp bass, barred sand bass, sculpins, yellowtail); sharks and rays (leopard sharks, shovelnose guitarfish); birds (cormorants, seagulls,, pelicans, terns) and marine mammals (dolphins, seals and sea lions). Good thing this species schools to make it more difficult to pick one off... because almost everything is after them! Well, except humans. The larger jacksmelt are a favored food over the topsmelt.

It was interesting to find that topsmelt schools composed of just one gender are observed. Now I taught at a segregated school and it got a lot more "exciting" (= challenging) when girls were allowed to enroll there! Maybe these single sex schools just want a little time to think about other things! Although some topsmelt become sexually mature during their first year, most wait until they are 2-3 years old. They may spawn in almost any month (much more fun than having just a short season). The female may produce 200 to 1,000 eggs each season. Rather than cast them into the water to be fertilized, this species is a demersal spawner which means they lay their eggs on the bottom attached objects like seaweed. The eggs have short adhesive threads that attach to the object. Males then enter and fertilize the eggs. Once the eggs hatch, the larvae are planktonic for a while before settling out in shallow water when they are about 1/4" long. If none of their predators get to them, a topsmelt may live eight or nine years.

© 2011 Dr. Bill Bushing. Watch the "Dive Dry with Dr. Bill" underwater videos on Catalina Cable TV channel 29, 10:00 AM 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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Individual topsmelt in kelp, school of topsmelt near surface; topsmelt showing bright lateral line and topsmelt out in the open at night.

This document maintained by Dr. Bill Bushing.
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