Stories tagged fish

Nov
09
2007

One weird little fishy.: The mangrove killifish, Rivulus marmoratus. Photo USGS.
One weird little fishy.: The mangrove killifish, Rivulus marmoratus. Photo USGS.

Researchers have found that the mangrove killifish, a two-inch-long fish common to Caribbean coasts, spends several months out of water, living in the hollows of trees. Most of the year, the fish live in muddy pools and are fiercely territorial. But during the dry season, they crawl into burrows carved into the trees by insects, pack themselves together tightly, and alters their metabolism to breathe air.

Oh, yeah, and the mangrove killlifish also has both male and female organs, so it can reproduce without a mate. This is one strange fish.

Oct
18
2007

Gone fishing?: Where have the walleye's gone on Minnesota's Lake Mille Lacs? Fall surveys this year show about half the number of fish in the state's "walleye factory" than typically are found. (Photo courtesy of the U.S. Fish and Wildlife Service)
Gone fishing?: Where have the walleye's gone on Minnesota's Lake Mille Lacs? Fall surveys this year show about half the number of fish in the state's "walleye factory" than typically are found. (Photo courtesy of the U.S. Fish and Wildlife Service)
The walleye is Minnesota’s state fish. And the No. 1 lake to catch walleyes in the state is generally considered to be Lake Mille Lacs. But fish population censuses conducted this summer on Minnesota’s walleye factory have fisheries managers scratching their heads.

You may have read or heard some of the headlines about this in recent days. Some of those reports sensationalized the situation. While the walleye numbers are down on the lake, they’re by no means at critical conditions, the Minnesota Department of Natural Resources (DNR) reports.

Routine testing done on the lake this summer corralled only about half the usual number of walleyes as the average number collected between 193 and 2006, the DNR says. The tests, conducted near shorelines are done annually to monitor fish populations and size.

“We expected some decline in walleye numbers based on a number of factors, including a weak 2004-year class of walleye,” said DNR Fisheries Chief Ron Payer. But the magnitude of this year’s decline was unanticipated.”

This year’s net catches averaged 7.2 walleyes per net compared to the 15.4 average from the previous 14-year average of 15.4 walleyes per net. Similar sampling done last year collected 20.4 walleyes per net.

So why the big drop?

Payer said that warm lake water, particularly in June, may have played a significant role in the drop. Warmer water temps stress fish and hooking mortality rate goes up as water temperatures go up, as well.

Is the situation critical?

Not yet, Payer said. But the reason the DNR does the annual walleye population survey is to gather data on setting limits for the coming fishing season. And there’s no doubt, he said, that those regulations will likely be tightened in 2008.

But he added that Mille Lacs still has a strong number of spawning-sized fish.

Payer said anglers should know Mille Lacs continues to hold good numbers of spawning-sized fish. Still, the new data means the DNR will need to revisit regulations to ensure the lake’s walleye harvest stays within the safe harvest level and the state’s allocation. No walleye harvest overage will be allowed in 2008 due to the lower than anticipated number of walleye in recent population assessments.

Because of several factors, Mille Lacs’ walleye population is regulated differently than other Minnesota lakes. Through a treaty with the Chippewa Indian bands negotiated in 1837, those bands have significant fishing rights on the lake. Those rights are taken into account with sport fishing limits each year in managing Mille Lacs’ walleye population.

This past year, sport anglers could only take four walleyes a day. They had to be between 14 and 16 inches in length, with the exception made for one walleye longer than 28 inches long. Earlier in the season, the limits were actually less restrictive, but heavy fishing success in the early part of the summer required tightening the Mille Lacs limits.

Regulations for the 2008 open water season will be established in February 2008 and go into effect with the walleye opener on May 12.

So do you have a theory on what's happened to the walleyes? Share your thoughts here with other Science Buzz readers.

Minnesota DNR press release on Mille Lacs walleye numbers

Aug
10
2007

A shark, doing it's best: Mostly he just wants to be left alone.    (photo by Mshai on flickr.com)
A shark, doing it's best: Mostly he just wants to be left alone. (photo by Mshai on flickr.com)
Scientists in New South Wales and Florida are testing a new method of measuring the biting force of a great white shark using computer models.

Attempts have been made to measure sharks’ biting force underwater, in captivity and in the wild, although these are known to provide inadequate results. Sharks will generally do weak a “test bite” before applying the full force of their jaws, and these test bites are generally all that’s measured.

In this new experiment, researchers are dissecting a 2.4-meter long great white shark, in part to make an extremely accurate computer model of its anatomy, and in part to drive home the point that the animal should have just allowed them to measure its bite while it was alive. Advanced computing methods, originally developed for “calculating stresses in structures such as bridges,” will then be applied to the model, and should provide a much more accurate range of the shark’s biting force.

This process contrasts sharply with my own, I believe, much more elegant test of shark biting power. There are several simple steps involved in my method: Step 1 – gather a variety of small to medium sized objects. Step 2 - Rate the hardness of these objects, not on an objectively quantified scale, but relatively (for example: The kitten is harder than the pillow, but not as hard as the dictionary). Step 3 - Take these objects to your nearest shark. Get the shark to bite the objects (this can be difficult, but the right combination of chum and verbal abuse should do the trick). You will then have a simple and easy to understand scale of shark biting strength (for example: the shark could crush the pillow, the kitten, the dictionary, and the cookie jar, but not the lawn mower engine). If you still feel, at this point, that you need a measurement that uses more universally accepted units, you can then crush similar objects by yourself, far away from the shark, using free weights, or forty-pound bags of dog food. These can then be easily converted into newtons, or pounds per square inch, or whatever your physics teacher requires.

If the computer model method proves to give reasonably accurate results, I suppose it will then be up to individual researchers to choose that method or mine. It will just depend on whether someone doesn’t want to get their hands dirty, or if they care about style and integrity.

Jul
25
2007

These three stories are all about weird fish.  No, not the restaurant in SF, but the wet kind.: Photo by lawgeek at flickr.com
These three stories are all about weird fish. No, not the restaurant in SF, but the wet kind.: Photo by lawgeek at flickr.com

I surf the web. I read the blogs. I see stuff that looks interesting, and I file it away, They accumulate, they reach critical mass, and they burst forth in full, horrendous flower.

Which is a roundabout way of saying, I’ve seen a few interesting articles on marine life lately, and rather than write three separate posts, I thought I’d wrap them all up into one.

Octosquid

Scientists in Hawaii have discovered a new deep-sea creature with the arms of an octopus and the mantle of a squid. Dubbed “octosquid,” it was caught in the filter of a deep sea pipeline.

Hungry squid invade California

Humboldt squid, a giant predator that can grow 7 feet long and weigh up to 110 pounds, has expanded its range into central California. It normally hangs out in tropical waters from Peru to Costa Rica. But fishing pressures have reduced its natural predators – tuna, swordfish and sharks – resulting in a squid population explosion. They have moved north into new territory. Humans, seals, otters and other mammals have nothing to fear, but the squid do eat large amounts of hake, anchovy and other commercial fish.

Sea monsters

Check out this photo gallery of weird, cool creatures of the deep.

The coelacanth (SEE-la-kanth) is a deep-sea fish that has survived unchanged for over 65 million years. It’s limb-like fins suggest it is closely related to the first land animals.

Oct
05
2006

Skipjack herring: Illustration courtesy Duane Raver and the U.S. Fish and Wildlife Service.
Skipjack herring: Illustration courtesy Duane Raver and the U.S. Fish and Wildlife Service.

I work at the Science Museum and I often learn unusual things during the course of my day. Some things are funny, some I store away to pull out in a Cliff Claven moment, and others make me want to run screaming to my desk to put them into this blog.

This is one of the latter.

Yesterday I learned that herrings may communicate with one another through their anuses by farting. I almost exploded when the person leading the meeting casually mentioned this fact. I ran back to my computer, and sure enough. Researchers at not one, but TWO institutions are studying the phenomena. Both the Institute of Coastal Research at the National Board of Fisheries in Sweden and the University of British Columbia, Vancouver have researchers looking into the matter.

Before this remarkable discovery, it was known that herrings communicated with one another through sounds produced by their swim bladder. Researchers thought that all the sounds they heard coming from the herring were coming from the swim bladder. But, and I am laughing as I type, they noticed that a stream of bubbles would leave the herring’s anus in time with the sounds they were hearing. Sure enough, they are connected, and that sound was soon dubbed by the quick-thinking researchers as a Fast Repetitive Tick (or FRT, if you will).

Researchers note that the unlike the gas we pass, these sounds are not produced by the digestive process, but rather a connection between the swim bladder and the anus. The exact purpose or reason behind the FRTs is not exactly known. One theory is that is a way for the herring to communicate with each other at night. Another is that is an anti-predator tactic. Seriously. Or, it could just be an incidental release of air from the swim bladder as the fish adjusts its buoyancy.

You can hear the herring communicating in this manner here.

Woah! Check out this creepy fish found down in Texas. It has human looking teeth. I can't find much more credible information on this fish but some are suggesting it might be a sheapshead. Any ideas?

Jun
08
2006


Canoeing on a Minnesota Lake: Courtesey zanzibar

Hey do you like to fish, canoe, or swim in Minnesota lakes? I can't imagine our hot humid summers without the relief of a dip in cool Lake Nokomis. But how are those wonderful lakes that make our state so unique doing? Well, our pals across the river at the Bell Museum of Natural History are hosting a cool event next week about just that:

CAFE SCIENTIFIQUE
Fishing for Trouble?

Tuesday, June 13, from 6 to 8 p.m., Varsity Theater, Dinkytown, Free

Deborah Swackhamer and Roland Sigurdson of the U's Water Resources Center will discuss the state of our lakes, including how chemicals can affect water quality, fisheries, and human health. The Café Scientifique event, hosted by the U's Bell Museum of Natural History, precedes a Thursday evening fishing trip with Sigurdson on the shores of Lake Como in St. Paul. To learn more about both events, call 612-624-7083.

Should be a cool event with some good discussion and a chance to get your questions answered. See you there.

May
01
2006


A model and a fossil show how Tikaalik Roseae might have lived in shallow stream beds about 375 million years ago.

What lived in water, could do push ups and might be the missing link in the evolution of sea creatures and land animals?

It’s Tiktaalik roseae, a crocodile-like creature that lived most of the time in the water, but ventured on land occasionally. Fossil remains of the large, nearly 400-million-year-old creature were recently found north of the Arctic Circle in Canada.

It’s the first solid fossil evidence that shows the transformation of aquatic animals into being land creatures. Tiktaalik specimens that were found range in length from four to nine feet long and look like a cross between a fish and a crocodile. They swam in shallow streams in what at the time, around 375 million years ago, was believed to be a subtropical climate. Tiktaalik were meat eaters.

The key that makes researchers believe it went up onto land is that Tiktaalik’s front fins had a bone structure that is much like a shoulder, upper arm, elbow, forearm and wrist. It’s believed the creatures would slither out of the water and pull themselves around on land much like seals do today.

The head structure of Tiktaalik is also a piece of evidence in the water-to-land evolution. It had a crocodile-like head, including eyes on top of the skull rather than on the side, like fish. It could also move its head independently of its shoulders like land animals can do today. But the creature’s jaws and snout were very fishlike. Researchers think it might have had both a set of lungs and gills for breathing. But like fish, it had scales and fins.

Scientists are planning to return to the Artic region to do further digging, but due to the cold climate there today, there is just a short window for doing field research. But much of what scientists are seeing in Tiktaalik confirms their guesses as to how water creatures could eventually convert to land animals.

The new findings were published in a recent edition of the journal Nature. Researchers have set up their own Tikaalik website with much more information about the discovery.