As reported in our April mail-out, and also in our blog Study of Shark and Ray Eggcases , one of our Facebook followers had been finding hardnose skate egg casings along the beaches from Goolwa to Bashams beach and then uploading photos and data to iNaturalist (see https://www.inaturalist.org/people/wyrsta ). To better identify what they find, they wanted to learn how to tell the difference between the egg casings of Hardnose skates and Thornback skates. They also wanted to find more general background information on what types of skates live in these areas (the beaches from Goolwa to Bashams beach).
They were hopeful that the egg casings that they were finding in good condition might suggest that the species is doing OK after the area had been hit so hard with the recent toxic algal bloom.
Up to the last week of March, they had found over 40 skate eggs on those beaches during that month.
We were able to assist this person by sending them details from past newsletters and journals that may be of some assistance. They appreciated our input and thanked us for those details.
The journal article in question was my 1993 article title “The Breeding of Sharks, Stingrays and Skates”.
Our colleague later told us that all the IDs for the egg casings that they had found came from iNaturalist, except for the obvious Port Jackson shark egg casings.
Front cover of our February 1992 newsletter and inside page about Port Jackson sharks
Where a journal article of mine had showed an egg casing as being for the Rusty Catshark, Parascyllium ferrugineum, iNaturalist identified the same looking egg casing as belonging to Varied Carpet/catsharks, Parascyllium variolatum (Carpetshark according to iNaturalist).
Our colleague reports that these carpetshark egg casings are the ones that they find the most. Some of these, however, are dark coloured and some are a honey colour. The colour difference is said to be very obvious, but iNaturalist still names both shades as being Varied Carpetshark eggs.
The egg casings for the Rusty Catsharks (also carpetsharks according to iNaturalist) are said to appear the same as the Varied Catshark. but they are much larger in size.
I found this Gulf Catshark, Asymbolus vincenti, in the shallows at Second Valley in 2014: –
The egg casings that iNaturalist identifies as Gulf Catshark, Asymbolus vincenti, eggs are said to appear to be the same as the Spotted Catshark, Halaelurus analis* in my journal article.
* (Now Grey Spotted Catshark, Asymbolus analis. According to WoRMS (World Register of Marine Species), the name Halaelurus analis is still being applied – “Halaelurus analis, commonly known as the Grey Spotted Catshark, is a species of shark found in the Indo-West Pacific region, particularly in Australia. It inhabits the continental shelf, ranging from close inshore to offshore, and is typically found at depths between 10 and 180 meters, with a preference for depths between 10 and 60 meters. This species is oviparous, laying paired eggs that are fed solely on yolk. The Grey Spotted Catshark is characterized by its rounded body, flattened head with a pointed snout, and gill slits that are lateral. It is a temperate species, with a preferred temperature range of 16.4 – 20.5 degrees Celsius, with a mean temperature of 17.9 degrees Celsius. The species is considered to have low resilience and high fishing vulnerability, indicating a need for conservation efforts to protect its population.”
Our colleague says that they do find a good number of these Gulf Catshark, Asymbolus vincenti, egg casings, but not as many as the Carpetshark or Skate egg casings.
Egg casings for the Elephant Shark also came into consideration. iNaturalist calls the Elephant Shark the Australian Elephantfish, Callorhinchus milii. Our colleague says that they have found 2 of these egg casings so far.
(I wrote about Elephant Fish in both our May 1988 and May 1993 newsletters.)
iNaturalist has since identified 2 skate egg casings as being Peacock Skate, Pavoraja nitida, egg casings. Our colleague didn’t think that there were so many different skates in SA.
This last page from my 1993 journal article lists the numerous references that were used for my article: –
(We thank our colleague for bringing this fascinating subject back to our attention.)