DIVE DRY WITH DR. BILL #675: BAITFISH BYE BYE?
This will be yet another column about the ecological dilemma we are experiencing in our local waters over the past year and a half. At least this time it will not be about the nasty "devil weed," Sargassum horneri, but about a more common ecological impact affecting kelp forest ecosystems. Yep, I'm referring to the "hot water" we're in.
I arrived on the island 47 years ago during a period of cooler water. Kelp forests were lush and I was warned to carry a big knife to cut myself out of it if I became entangled. Well, I found that wearing that big knife resulted in a greater frequency of getting caught... and it was of no use in fending off the great white sharks I feared back then since none appeared close enough for me to stab my buddy and swim away as fast as I could.
Then in the 1970s I experienced my first el Niño followed by several severe events in 1982-84 ,1987-88, 1997-98 and the current one. During all of these, our kelp forests were decimated and our waters became as clear as the tropics due to the lack of nutrients and low plant plankton productivity. I've written often about the sharp decline in giant kelp productivity following periods when the water was warmer than 68° for longer than a week or two. Low nutrients also affect phytoplankton, although not necessarily with the same temperature tipping point.
Over the past 20 months I've only occasionally seen baitfish in our waters, and then mostly at night. My assumption has been that the warm waters reduced plankton growth, thus reducing the food available for these ram filter feeders. Certainly visibility at times has been exceptional, suggesting that plant plankton concentrations are low. Yet, there are still large schools of blacksmith in our waters suggesting that there is an ample supply of plankton for this species. I must admit I'm a bit stumped by this... almost as much as I am by the female of our species!
With baitfish being mostly absent at least from our nearshore shallower waters, I have also not observed many barracuda. In past years when baitfish were plentiful, I'd often see small schools of these predators attacking the jack mackerel, chub mackerel, anchovies or sardines. One year while diving the park with Scott Patterson we even encountered a huge school of barracuda numbering in the hundreds, although I think that was related to mating rather than munching.
The warm waters have allowed one baitfish predator, the yellowtail, to remain here well into the winter months. On a recent dive I had a school of about 14 youngsters circle me to see if I was edible or carrying a speargun (not in City waters and especially not the dive park!). They like the warm water, but still need to munch on something. Instead of a plentiful baitfish buffet, the yellowtail are chowing down on blacksmith which have little protection due to the absence of our giant kelp.
So where are the baitfish? I have heard reports from anglers that they are being seen in deeper, cooler waters offshore. But why? Do they prefer the cooler waters to our abnormally warm temperatures near shore? Or is there a more nutrient-rich environment there where plankton are more abundant (at least within the zone of light penetration)? Of course I'd like an answer to those questions, but I think for the time being I'll enjoy the warmer water along shore!
© 2016 Dr. Bill Bushing. For the entire archived set of over 650 "Dive Dry" columns, visit my website Star Thrower Educational Multimedia (S.T.E.M.) Home Page
Image caption: School of jack mackerel and large school of blacksmith; Pacific barracuda and yellowtail in dive park.
This will be yet another column about the ecological dilemma we are experiencing in our local waters over the past year and a half. At least this time it will not be about the nasty "devil weed," Sargassum horneri, but about a more common ecological impact affecting kelp forest ecosystems. Yep, I'm referring to the "hot water" we're in.
I arrived on the island 47 years ago during a period of cooler water. Kelp forests were lush and I was warned to carry a big knife to cut myself out of it if I became entangled. Well, I found that wearing that big knife resulted in a greater frequency of getting caught... and it was of no use in fending off the great white sharks I feared back then since none appeared close enough for me to stab my buddy and swim away as fast as I could.
Then in the 1970s I experienced my first el Niño followed by several severe events in 1982-84 ,1987-88, 1997-98 and the current one. During all of these, our kelp forests were decimated and our waters became as clear as the tropics due to the lack of nutrients and low plant plankton productivity. I've written often about the sharp decline in giant kelp productivity following periods when the water was warmer than 68° for longer than a week or two. Low nutrients also affect phytoplankton, although not necessarily with the same temperature tipping point.
Over the past 20 months I've only occasionally seen baitfish in our waters, and then mostly at night. My assumption has been that the warm waters reduced plankton growth, thus reducing the food available for these ram filter feeders. Certainly visibility at times has been exceptional, suggesting that plant plankton concentrations are low. Yet, there are still large schools of blacksmith in our waters suggesting that there is an ample supply of plankton for this species. I must admit I'm a bit stumped by this... almost as much as I am by the female of our species!
With baitfish being mostly absent at least from our nearshore shallower waters, I have also not observed many barracuda. In past years when baitfish were plentiful, I'd often see small schools of these predators attacking the jack mackerel, chub mackerel, anchovies or sardines. One year while diving the park with Scott Patterson we even encountered a huge school of barracuda numbering in the hundreds, although I think that was related to mating rather than munching.
The warm waters have allowed one baitfish predator, the yellowtail, to remain here well into the winter months. On a recent dive I had a school of about 14 youngsters circle me to see if I was edible or carrying a speargun (not in City waters and especially not the dive park!). They like the warm water, but still need to munch on something. Instead of a plentiful baitfish buffet, the yellowtail are chowing down on blacksmith which have little protection due to the absence of our giant kelp.
So where are the baitfish? I have heard reports from anglers that they are being seen in deeper, cooler waters offshore. But why? Do they prefer the cooler waters to our abnormally warm temperatures near shore? Or is there a more nutrient-rich environment there where plankton are more abundant (at least within the zone of light penetration)? Of course I'd like an answer to those questions, but I think for the time being I'll enjoy the warmer water along shore!
© 2016 Dr. Bill Bushing. For the entire archived set of over 650 "Dive Dry" columns, visit my website Star Thrower Educational Multimedia (S.T.E.M.) Home Page
Image caption: School of jack mackerel and large school of blacksmith; Pacific barracuda and yellowtail in dive park.
