Marine biologist questions

[The Suit]

Just got back from a few days offshore fishing in Guatemala and saw a few things that made me curious:

- We were fishing around a pod(?) of spinner dolphins when all of a sudden they all started swimming fairly fast in the same direction, rolling on the surface and beating it into a froth. It almost looked like they were in a v-formation. There were hundreds of them in evidence. Any ideas why they'd do that?

- I didn't get a picture of the spinners doing that because almost as soon as they started, our flatlines got blasted by a couple of 30-40 lb. yellowfin tuna. When we cut open their stomachs, they were full of small (shells 2" across) crabs. This was 30 miles offshore, in over a 1000 feet of water. Where the heck did those tunas go to fill their bellies with crabs?

[Hutch]

IS ANYONE HERE A MARINE BIOLOGIST?!?!?

[Dexter Rutecki]

Damn you, Hutch. But since I already looked after seeing the thread title:

[XXX-er]

J Where the heck did those tunas go to fill their bellies with crabs?

you sure it wasn't krill ?

fish sometimes herd them, I have seen flocks of birds out on the north coast l cooperate to hunt even birds of different species

[ak_powder_monkey]

Just got back from a few days offshore fishing in Guatemala and saw a few things that made me curious:

- We were fishing around a pod(?) of spinner dolphins when all of a sudden they all started swimming fairly fast in the same direction, rolling on the surface and beating it into a froth. It almost looked like they were in a v-formation. There were hundreds of them in evidence. Any ideas why they'd do that?

they were either playing, dolphins like to play or they were trying to herd/stun prey

- I didn't get a picture of the spinners doing that because almost as soon as they started, our flatlines got blasted by a couple of 30-40 lb. yellowfin tuna. When we cut open their stomachs, they were full of small (shells 2" across) crabs. This was 30 miles offshore, in over a 1000 feet of water. Where the heck did those tunas go to fill their bellies with crabs?

tuna can swim like 60 miles an hour... Also I imagine theres a lot of crabs on various bits floating debris out there. Coulda been krill or something pelalgic too... Also them diving to the bottom isn't like out of the question

disclaimer, I am not a Marine Biologist

[Hutch]

disclaimer, I am not a Marine Biologist

You'll never get laid with this attitude.

[hop]

Just got back from a few days offshore fishing in Guatemala and saw a few things that made me curious:

- We were fishing around a pod(?) of spinner dolphins when all of a sudden they all started swimming fairly fast in the same direction, rolling on the surface and beating it into a froth. It almost looked like they were in a v-formation. There were hundreds of them in evidence. Any ideas why they'd do that?

- I didn't get a picture of the spinners doing that because almost as soon as they started, our flatlines got blasted by a couple of 30-40 lb. yellowfin tuna. When we cut open their stomachs, they were full of small (shells 2" across) crabs. This was 30 miles offshore, in over a 1000 feet of water. Where the heck did those tunas go to fill their bellies with crabs?

Eastern spinners are night feeders so whatever behavior they were doing was probably not related to feeding. I will also mention that interpreting cetacean behavior w/o knowing all of the potential influential factors is near impossible. Even if I was on the boat watching them try and evade a predator I could also see, I'd probably be reduced to "uhh, I dunno what they're doing or why".

Pelagic crabs are common and an extremely important food source for just about everything down there. Here's a link for you. Pleuroncodes planipes look kind of micro-lobster-esque, but I've also seen others that look more like a typical crab. Also, certain species of crab larvae develop offshore; the little buggers float around out there until they get big enough to sink and move back to their more coastal environment.

I took this photo of rough-toothed dolphins somewhere on the Blake Plateau off the east coast this summer, where the water's ~500m deep. Check out the lower left.

[ak_powder_monkey]

You'll never get laid with this attitude.

Last time I got laid I took her back to my place and taught her how to tie a woolly bugger

[The Suit]

Thanks, Hop. I did not realize there was such a thing as a pelagic crab. I think what we saw was more crab-like than Pleuroncodes planipes - more like the guy in your picture.

Patrick - no need for the disclaimer.

[warthog]

Here is a long delayed answer from my friend's wife. She is a Marine Mammal Necrologist with NOAA.

"Stenella longirostris commonly swim in large groups numbering in the hundreds, so that behavior is not uncommon. As for crabs in tuna stomachs, crabs do have a pelagic life stage.. those tuna probably found and ate them during this vulnerable period."