The points made above about breathing more deeply are physiologically important. You normally have a modest volume of "dead space" that doesn't contribute to oxygen/CO2 exchange (pharynx, trachea, bronchi). When you are wearing scuba gear, there is additional dead space in your second stage.
Many divers trying to decrease their air consumption start "sipping" little breaths, trying to "not waste gas". This turns out to be the opposite of what should be done, because with small breaths, the fraction of the breath that is wasted on dead space is larger than with a bigger volume breath, where more of the breath gets down deep into the alveoli.
Scuba breathing, especially at depth, should be slow (avoid turbulent air flow with its increased resistance), somewhat deeper (to compensate for extra dead space without affecting buoyancy too much), and with a similarly increased exhalation (to dump CO2). In compensation, absent vigorous exercise, your breaths per minute will not be as frequent as at the surface. But once you have the technique down, you won't even think about it any more.
With that technique, plus streamlining and optimal weighting, you'll find your air consumption will improve markedly.
Dive safe!
Diving Doc
Many divers trying to decrease their air consumption start "sipping" little breaths, trying to "not waste gas". This turns out to be the opposite of what should be done, because with small breaths, the fraction of the breath that is wasted on dead space is larger than with a bigger volume breath, where more of the breath gets down deep into the alveoli.
Scuba breathing, especially at depth, should be slow (avoid turbulent air flow with its increased resistance), somewhat deeper (to compensate for extra dead space without affecting buoyancy too much), and with a similarly increased exhalation (to dump CO2). In compensation, absent vigorous exercise, your breaths per minute will not be as frequent as at the surface. But once you have the technique down, you won't even think about it any more.
With that technique, plus streamlining and optimal weighting, you'll find your air consumption will improve markedly.
Dive safe!
Diving Doc