Pelorus Sound is typical of New Zealand coastal locations, i.e. there is a semi-diurnal tide modulated on a spring-neap cycle, generated by the superposition of M2 (lunar, semi-diurnal) and S2 (solar, semi-diurnal) tidal constituents. Other tidal constituents, notably N2 (semi-diurnal, generated by the ellipticity of the moon’s orbit), introduce further modulation, meaning that the spring-neap cycle is not exactly repeated. The tidal range varies between at neap and at spring. (These values are calculated from a sea level time series, July 1997 – February 1998, at Pelorus Sound entrance.) The propagation of this tidal signal into Pelorus Sound has not been well
Threats to sea turtles Fisheries often use large-scale nets and hook systems that are indiscriminate and catch whatever comes along, be it sea turtle, dolphin, or even shark. What is known as “bycatch” is a large contributor to sea turtle deaths, as seen in Baja California. Longline, trawl, and gillnet fishing are three types of fishing with the most sea turtle accidents. Deaths occur often because of drowning, where the sea turtle was ensnared and could not come up for air. Another dangerous aspect of fishing that is common is when sea turtles inadvertently swallow sharp hooks, which can get stuck within the soft