I drafted the following for my newspaper column column "Dive Dry with Dr. Bill." It is what it states... a hypothesis, unproven and untested that suggests possible causes for the horrible visibility in SoCal and the increase in sightings of great whites.
I'd be interested in comments from anyone on ScubaBoard since it will not go to press for two weeks. Thanks
Dr. Bill
DIVE DRY WITH DR. BILL: MY HYPOTHESIS ABOUT THIS SUMMER
This is one summer I would have preferred to spend in Hawaii or Thailand or the Caribbean. The water is warm and clear there. Not only did our local economy dip a bit, the diving conditions were the worst I can remember in 35 years of on-again-off-again diving on Catalina. Long-term divers I've spoken with agree. If I didn't have to get my gills wet every few days, I might not have dived most of the summer. Of course I also have to keep my dive buddies happy, don't I ladies?
Local and visiting divers have asked me, as a marine biologist, why we're experiencing such poor visibility and winter-like temperatures. This weekend I was lucky to see 10-12 feet ahead of me and the temperature dipped to 55 degrees on one dive- and I wasn't that deep. This time of year we should be experiencing our warmest waters and good visibility. After months of watching this nonsense, I have formed a hypothesis that not only explains the conditions but also the increased sightings of great white sharks. Read on.
A scientific hypothesis is actually just a theory based on a set of experiences in the "real" world. I'm referring to underwater, not the world of jobs and commerce... of which I obviously know little. One takes a set of observations and formulates a theory to explain the causes. My Funk & Wagnalls (yes, I actually own one) defines an hypothesis as "an unproved scientific conclusion drawn from known facts." "Let's look at the facts, ma'am," as Sergeant (Detective) Friday used to say.
The poor visibility ("vis" in diver terminology) appears to be caused by plant material such as phytoplankton due to the strong green color. Phytoplankton blooms are not uncommon along our coast as daylength increases and colder waters bring nutrients from deeper water. Plants need sunlight and nutrients (marine plants already have plenty of water of course). Normally these blooms last a week or two. This year they seem to have lasted forever. Why? Water temperatures were abnormally low earlier this summer. Colder water contains more nutrients than warmer water. Therefore abundant nutrients in the water column and increasing daylength allowed longer plankton blooms.
As the summer progressed, surface temperatures suddenly jumped up 5-10 degrees in a short time (two weeks). This warming should have resulted in depleted nutrients. However we had a thermocline (the abrupt boundary between warm and cold water masses) that was fairly shallow- as little as 17 feet based on my dive computer readings. This thermocline rose and fell throughout the entire summer. When cold water rose higher, it replenished nutrients in the surface waters and maintained the plankton bloom for weeks on end. Visibility has generally been worse in the upper 40-60 feet wher sunlight is strongest.
We've also had a lot of surge throughout the summer, not just during hurricane season off Baja. At times I've felt I was in a winter storm underwater with strong surge tearing seaweeds, even large ones, from the rocks. The rapid increase in water temperature in August also triggered a quick die-off of kelp near the surface, a natural but usually slower process during the gradual warming in a normal summer. Lots of seaweed and kelp detritus covered the ocean floor where it was ground into small particles by the surge and abrasion. This explains the presence of a lot of particulates in the water in addition to phytoplankton, further decreasing "vis."
So how do the great white sharks fit in? Poor visibility appears to cover much of the southern California coast and extends almost to San Clemente Island (they had 100 foot visibility a short while ago). Now even when I'm diving in the Dive Park under low vis, I often have to surface to get my bearings since I can't see my usual landmarks if they are more than 10 feet away. Perhaps the great whites are experiencing a similar problem and need to surface to get their bearings... or their sea lions. This may also help explain the fatal attack at Avila Beach.
Of course hypotheses should be tested using the scientific method before being accepted as scientific "fact." Should some foundation wish to fund the research, say to the tune of a quarter million dollars (okay, how about $25,000? a measely $250???), I'd be happy to test this hypothesis. Makes more sense than funding research to prove whether reducing the minimum wage creates more jobs... or just more poverty. Until my hypothesis is properly tested, it will remain my educated opinion. Take it or leave it.
© 2003 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.
I'd be interested in comments from anyone on ScubaBoard since it will not go to press for two weeks. Thanks
Dr. Bill
DIVE DRY WITH DR. BILL: MY HYPOTHESIS ABOUT THIS SUMMER
This is one summer I would have preferred to spend in Hawaii or Thailand or the Caribbean. The water is warm and clear there. Not only did our local economy dip a bit, the diving conditions were the worst I can remember in 35 years of on-again-off-again diving on Catalina. Long-term divers I've spoken with agree. If I didn't have to get my gills wet every few days, I might not have dived most of the summer. Of course I also have to keep my dive buddies happy, don't I ladies?
Local and visiting divers have asked me, as a marine biologist, why we're experiencing such poor visibility and winter-like temperatures. This weekend I was lucky to see 10-12 feet ahead of me and the temperature dipped to 55 degrees on one dive- and I wasn't that deep. This time of year we should be experiencing our warmest waters and good visibility. After months of watching this nonsense, I have formed a hypothesis that not only explains the conditions but also the increased sightings of great white sharks. Read on.
A scientific hypothesis is actually just a theory based on a set of experiences in the "real" world. I'm referring to underwater, not the world of jobs and commerce... of which I obviously know little. One takes a set of observations and formulates a theory to explain the causes. My Funk & Wagnalls (yes, I actually own one) defines an hypothesis as "an unproved scientific conclusion drawn from known facts." "Let's look at the facts, ma'am," as Sergeant (Detective) Friday used to say.
The poor visibility ("vis" in diver terminology) appears to be caused by plant material such as phytoplankton due to the strong green color. Phytoplankton blooms are not uncommon along our coast as daylength increases and colder waters bring nutrients from deeper water. Plants need sunlight and nutrients (marine plants already have plenty of water of course). Normally these blooms last a week or two. This year they seem to have lasted forever. Why? Water temperatures were abnormally low earlier this summer. Colder water contains more nutrients than warmer water. Therefore abundant nutrients in the water column and increasing daylength allowed longer plankton blooms.
As the summer progressed, surface temperatures suddenly jumped up 5-10 degrees in a short time (two weeks). This warming should have resulted in depleted nutrients. However we had a thermocline (the abrupt boundary between warm and cold water masses) that was fairly shallow- as little as 17 feet based on my dive computer readings. This thermocline rose and fell throughout the entire summer. When cold water rose higher, it replenished nutrients in the surface waters and maintained the plankton bloom for weeks on end. Visibility has generally been worse in the upper 40-60 feet wher sunlight is strongest.
We've also had a lot of surge throughout the summer, not just during hurricane season off Baja. At times I've felt I was in a winter storm underwater with strong surge tearing seaweeds, even large ones, from the rocks. The rapid increase in water temperature in August also triggered a quick die-off of kelp near the surface, a natural but usually slower process during the gradual warming in a normal summer. Lots of seaweed and kelp detritus covered the ocean floor where it was ground into small particles by the surge and abrasion. This explains the presence of a lot of particulates in the water in addition to phytoplankton, further decreasing "vis."
So how do the great white sharks fit in? Poor visibility appears to cover much of the southern California coast and extends almost to San Clemente Island (they had 100 foot visibility a short while ago). Now even when I'm diving in the Dive Park under low vis, I often have to surface to get my bearings since I can't see my usual landmarks if they are more than 10 feet away. Perhaps the great whites are experiencing a similar problem and need to surface to get their bearings... or their sea lions. This may also help explain the fatal attack at Avila Beach.
Of course hypotheses should be tested using the scientific method before being accepted as scientific "fact." Should some foundation wish to fund the research, say to the tune of a quarter million dollars (okay, how about $25,000? a measely $250???), I'd be happy to test this hypothesis. Makes more sense than funding research to prove whether reducing the minimum wage creates more jobs... or just more poverty. Until my hypothesis is properly tested, it will remain my educated opinion. Take it or leave it.
© 2003 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.
