A study, carried out in Argentina, shows correlation between seawater temperature variations and changes in the plasma levels of three sex steroid hormones, related to reproduction of the narrownose smooth-hound shark (Mustelus schmitti).

Temperature measured every 10 minutes 
Bottom water temperatures were registered every 10 minutes with the Star-Oddi Starmon mini temperature logger, and 123 pregnant and non-pregnant adult female sharks were sampled every other month. The sharks were caught by longline or rod and reef fishing. Shortly after capture, blood samples were taken to measure sex steroid levels.

Higher seawater temperature may affect reproductive events
The shark’s sex steroids levels, i.e. testosterone, estradiol and progesterone, were found to fluctuate depending on water temperature and reproduction cycle among the female sharks.

Before ovulation, for instance, the testosterone plasma levels declined with seawater temperatures below 13°C but were raised with a distinct elevation above 17°C. The measurements of estradiol showed the exact opposite. This indicates that higher seawater temperature could be a factor that triggers reproductive events such as ovulation and mating in elasmobranchs, i.e. sharks and rays.  

The study was conducted by Instituto Nacional de Investigación y Desarrollo Pesquero, Instituto de Investigaciones Marinas y Costeras, Centro Para el Estudio de Sistemas Marinos, University of Tasmania, and Instituto Tecnológico de Chascomús. It was published in General and Comparative Endocrinology in August 2019 and can be accessed here.

Picture: www.shark-references.com